Scaly, scabby scrotum

[Nanno]

Our buckling, Rambo has had this skin condition on his scrotum which I wonder if anyone else has dealt with. He's had it since probably sometime in November and it didn't look too bad for a long time so I was hoping it would go away by itself. For a long time it just looked like the bottom tips of his testicles were bald, but sometime in December it began to spread pretty rapidly upward, the skin became thick and crusty, and the hair began to clump together and fall off. I treated him twice already with Ivermectin (he'll get a third dose next week) in case it's some kind of parasite. I even put Ivermectin directly on the skin last month but it didn't seem to do any good. I ordered in some Nu-Stock sulfur ointment last week and have been applying that. It seems to be helping because the skin appears to be softening again and I don't see any new scabby areas appearing. The hair has not started growing back yet. But while I seem to have it under control now I'm curious what it is and whether anyone else's bucks have had something similar. About two weeks ago the tips of Rocky's testicles suddenly went bald so I wormed him and applied Nu-Stock right away. He's got some hair growth back already but I'm still feeling a few little scabby things under it. Any ideas?