Help! Chin with Heart Murmur?

My precious chinchilla, Cotton (11.5 years old) - Last Friday was lethargic, did not eat much and seem to having difficulty breathing. Occasionally he stretches his head out and there's a click sound when he breathes in. I later on noticed that he was actually breathing from his mouth when he does that.

I quickly made a trip down to the vet on Saturday morning 23/1.

The technicians there saw that he had labored breathing, immediately put him under oxygen therapy. The vet observed that there were fluids in the lungs and some murmur. After about 1.5 hours of oxygen therapy, the vet came back, Cotton's longs were clearer then went in with the stethoscope and been diagnosed that he has grade 6 heart murmur.

Vet prescribed the following:
1. Furosemide 0.05ml once a day.
2. Fortekor (Benazepril) 0.1ml once a day
3. Critical care
4. Suggested me to buy an oxygen tank in case he is seen having difficulty breathing.

24/1 Sunday:
He is still has labored breathing. He stopped eating on his own. At first he liked the critical care so I was able to feed him by spoon. Generally lathargic all day. Little to no poo.

25/1 Monday:
Thought things were looking up when he started eating hay and pellets on his own. Still see the labored breathing and I ordered an oxygen concentrator in case he is out of breath. Turned on the oxygen concentrator for a few hours in the day. Not much poop again.

26/1 Tue - 27/1 Wed:
He stopped eating again, similar breathing issues. Ordered some food from Fuzzies Kingdom and Tanya also advice that if he wasn't eating, to grind some alfafa, oats and mix with warm water. Thankfully he took this gladly but wouldn't take a whole lot of it either. Still very little poop

28/1 Thu:
Tried force feeding Cotton with critical care in a syringe, and boy it was difficult. I am not sure how to get 30ml into him at minimum. His face kept avoiding the syringe at some point. And occasionally he had to breathe through his mouth during the feed which got me worried as to whether I would choke him. He tries to forage around but has to take his time to chew and swallow or he gets out of breath again. I decided to go to another vet for a second opinion.

Today:
Woke up today seeing the hay bowl ruffled a little bit. He pooped alot more today but they were still tiny hard poops.
Went to the new vet and she diagnosed Cotton having Grade 3 murmur which got me confused now whether to believe the first vet or the second. She suggested increasing the dosage for Furosemide to 0.10ml twice a day as the earlier dosage was too little.

Also I have been reading forums and found out that it is difficult to diagnose a murmur, does anyone know how does a murmur get diagnosed and confirmed by a vet typically?
Cotton's been with with me for 10 years and I just can't bear to see him like this. He used to be so energetic..

Sorry for the long post but any comments from you guys is highly appreciated.

The clicker ticker, the murmur is on the mitral valve. Its "normal" for the furomsemide dose to have to be tinkered with until its balanced for that particular chin and symptoms are relieved. Murmurs with congestive heart failure can be treated successively and the chin can lead a normal life on the meds.

This happened earlier on, when I wrapped him up "burrito style" and trying to force feed him with the CC.
He had difficulty breathing and I can see him gasping for air through his mouth.. Video here - https://www.youtube.com/watch?v=GQRAT2_0k4c

Every time he breathes like that he makes a "click" sound. And it happens more frequently when he's eating or running about.. Any idea why?

Poor baby! Did you take him to the vet? (Since the video was taken)

When a chinchilla breathes through its mouth something very serious is going on, this is beyond the murmur issue, it looks like its last breaths, if the chin has not made it back to the vet it needs to go like yesterday.

Last 2 weeks were crazy for me. I was so worried for Cotton. I went to the first vet who said it was due to heart murmur and liquid in the lungs.
After 1 week of the medication, Cotton's situation still didn't improve! So I went to another vet last Friday 29 Jan in hopes to seek a second opinion, turned out the vet I made appointment with had to take urgent leave!!! And I was left with a less experienced vet who didn't know much about exotic pets. She deduced Murmur as well and that his lungs were clear. I didn't believe her - I saw that he wanted to forage in the hay and wanted to touch his pellets, but every time he went there, I observed it seemed like his lungs got so irritated and he just couldn't continue smelling his food.
I immediately made another appointment the next day (same day I posted the video) with another vet recommended by one of the pet shops.
The 3rd vet deduced that he had pneumonia and quickly injected him with antibiotics. Prescribed Baytril once a day and have him go on furusemide for higher dosage - 0.10ml and 3 times a day.
Few hours after the injection, he was bouncier and looked a little better. I think he responded well to the medication so the vet was probably spot on with the pneumonia. I put him on oxygen therapy every now and then. The initial few days with Baytril however was terrible - trying to feed him Critical care and making sure his gut is still active with Metalon, Cisapride and Probiotics. I couldn't really try to force feed him for fear of aspiration and making the Pneumonia worse, so had to entice him with pumpkin or applesauce layered over the critical care.
Now 6 days after Baytril he's breathing better, I see him eating on his own and pooping alot more - though the poop still not up to his original size.
He's brighter now - yesterday and today morning he's hopped out of his cage on his own for some out-of-cage activity time with no breathing difficulties!
I am thrilled and happy to see that he's better now but still monitoring his progress closely. Imagine the poor thing battling Pneumonia without antibiotics for a week! . I have to say he's a pretty strong boy. Phew..
Had an xray done for him 2 days ago and the vet confirmed he has an enlarged heart. Vet said he will need to be on Furusemide medication long term, and I hope Tanya's heart remedy formulae will be able to help his heart as well.

Cotton has had a relapse again and is not eating. Noticed him sneezing 5 times when I was just sitting there for 30 mins .

I am still continuing the Baytril, but meanwhile his appetite went down again and lost another 10g in one day. He isn't pooping at all for the entire day. I fed him CC / EFL and gave him some tummy rubs and exercise. Saw 1 or 2 really perfectly shaped poops in the cage after that. Is that a good sign?