I think the bike will explode. But I've been known to be wrong on this stuff.
Seriously - I lost a cap awhile ago, so I just "waterproofed" the swing arm with a bunch of grease then wiped it down. It's fine so far. I thought about making a cap instead of buying one. I was considering using tin snips to cut out the bottom of a soda can, then using silicone to put it on. Never got around to it though.
MF Battery, Iridium Plugs, RR relocated, Voltmeter, 170/80/15 Kenda Kruz rear tire, DIY Samsonite hard bags, DIY shaved seat with Beaded seat pad ('cause that's how I roll) and the dreaded STATOR CHANGE.
Shining Black Bess '86 VN750, retired for parts after a fried stator and being knocked (kee-runch) in her parking spot.