It could be a few things to be honest - a good reptile vet would be my first port of call if he was mine. I'd guess either impaction or infected hemi-pene.

And, I know this sounds harsh and restrictive, without a quarantine protocol you shouldn't really be looking to breed him this year anyway.

It's one of those rules that sound silly and ultra-cautious until you have a few snakes with problems come in and potentially lose you your whole collection though.