That picture of the broken cases of your 500 - the best advertisement for a decompression system you can find!
The type that Jar944 and others use, is a simple, cheap, no weld / bugger-all effort solution. My solution, is more expensive / involved.
Of course, you could be a 'hard man' and say "I don't need no frigging Decomp" - but your wallet will argue with you (especially if the breakage extends into the main case - if so, hopefully it can be welded / repaired - just pay a lot of attention to the correct alignment of the various shaft / bearing holes ), and you'll also be ID'ing yourself as a bit of a Drongo. What's not to love about an easier to fire up bike?
Oh, a better KS lever stop on the foot peg, can help, as well.
As for the WP area rot, Magnesium protected only by a bit of paint (if that) and water, especially under turbulence / cavitation - not a good idea. Yuck!