Got A Vet Involved, Just Looking For Others With Experience With This

So my 5 year old California Red Sided developed a lump just after his vent: https://imgur.com/gallery/hauNPyj

Took him to the vet yesterday, and after drawing samples from the lump it seems his musk gland (dunno the scientific term) is blocked.
They're sending the samples to a lab to find out what they can about the cause.
Has anyone dealt with this before? Any insights into cause and prevention?
He seems to be able to eat, poop and probably shed (hasn’t come up yet but last one was fine), but can’t musk when scared.

He's on a fuzzy mouse diet, and lives on aspen bedding with caves and logs for hides, and a heat pad and heat rock, and a “shed” rock that has some rougher edges to rub against.

I’m planning on getting him and his new friends into a bioactive setup once his new friends are big enough to live with him.
They’re so small and he hasn’t been around other snakes in 5 years, so right now they’re perfect food size to him, and I do t want to risk it.

Thanks!

The Vet. should have drained it, in my opinion. Making sure the substrate is clean is important but sometimes infections happen. Warm water soaks could help the blockage drain.

Can you post a photo of this from the underside? Thanks.

Here’s some photos of his belly: https://imgur.com/gallery/vGlSIUo

The vet did draw out extra fluid to relieve some pressure for him, but it had to be done with a needle. He couldn’t get it to drain any other way.
Hopefully get the lab results tomorrow, but I’ll give him a warm bath, too.

Looks like a classic musk gland blockage.

We’re trying a warm bath now. Sounds like it could take more than one to unblock.