Update: took him to a specialized vet (from a member rec).
She said he looked good, aside from a little dryness. I'm going to start doing some warm water soaks with him weekly to make sure he's hydrated well.
Got some bloodwork done to make more certain that he was doing well and everything came back great so far. Calcium levels are great, she said she sees no signs of any metabolic bone disease, he has very strong grip and the only bump of concern was on his arm, but she's not sure it's necessarily a cause for concern. She said it could be a lot of things, could be a benign tumor, or something else but it's really hard to know without something more invasive. So we're keeping an eye on that to see if it changes at all. Still waiting on further blood test results that could provide a few answers there.
She thinks the casque issue was most likely the result of a burn, probably not the sun, but a time when he climbed to close to the lights and touched his head to the mesh beneath a lamp. He likes to climb on the mesh walls, but I'm going to get some lamp stands to take them a little farther from the cage.
His kidneys are apparently doing fantastic for his age (almost 3).
TLDR: his overall health is great, his casque has healed well, and humidity is the main point of concern that I have actionable steps to fix.
The original pics I posted weren't very flattering, this is more of what he usually looks like. This is from today.
