I can't tell you how many times I have heard..but he was nuetered...and he doesn't have his balls, we hear that at least once a week here, The "balls: as you say sit up out of sight most of the time in many males. If I didn't know better I would believe most of my males to be nuetered. So either you have an unuetered male or your female has pyometria.
Thing with pyometria is when she is open there is a discharge, if she closes it is a closed infection with no discharge so maybe she just closed, Watch her all you want she will act normal until it is too late. Good breeders and owner miss these infections because chinchillas hide illness until they are on deaths door. So wait since you plan on it any way, wait and if you are wrong and something is wrong you will watch your new chinchilla die.
Maybe you will be lucky and it will be nothing, but heat discharge is little to no dishcharge, even a mating would not give her a wet belly. Urine will not give her a clear slimy belly, something is going on...If you wait it will be too late. It is ultimatly your choice though. If it is something then it is on you for not taking her to the vet since you don't know what you are seeing
