Rebuilding 1990 Trail Boss 2×4, with questions

I have a 1990 2×4 Trail Boss. I bought it for my wife knowing it had low compression. I was able to make it run, but not easily or reliably, so off with the jug. I should be picking it up next week, so re-assembly shall begin. I am doing some repainting of racks and some various trim to make it more "her" bike. I pulled the clutch cover and removed the engine from the frame. I got the clutch off and replaced that crank seal, still have to get the flywheel off to replace that crank seal. I am trying to clean the thing as much as I can before giving it to her, so the rear plastics are off and the frame is gonna get a good wash down. I am new to belt drive quads, but I have read a few things about getting the belt wet. I don’t remember any kind of seal being in the clutch cover, so is there supposed to be? This bike isn’t going to be rode in mass amounts of water, maybe not even mud, so I don’t think it will need to be super water tight, but if there needs to be some sort of seal, we can do that.
Another question, on the seal between the case and jug, does there need to be sealant used, or just the gasket? I know a good air tight seal is necessary in the crankcase, just want to make sure I get that.
Another question I have, what is the purpose for the knob on the side of the brake caliper on the trans? I can’t figure out any point to that things existence!

ROb