Yes, PLEASE take a stool sample to the vet...that is NOT normal, there is something going on there. I've raised these snakes in the past & still currently have 3-
their stools aren't noticeably stinky when they are healthy. And you even said he is always on the thin side...not normal!
And for what it's worth, this is likely the reason we're getting opposing opinions about the same kinds of other snakes here too. If you have ANY kind of snake whose
stool makes you gag, it's not normal & please do get it checked & treated.