So here's how it plays out. Turns out this was
not a powerspline crankset, but a square taper (bad assumption on my part-- awesome though, I don't feel so motivated to scrap the whole thing).
When I took off the left side crank the retaining fastener was barely finger tight, and the problem became immediately clear. Pictures:
Left crank, back side
Pretty much ruined...
Left crank, front side
The little ridge visible inside the bore is pushed up metal, not grease or dirt.
Taper/Bolt
The bolt seems to be unaffected.
Right side crank/rings
The right side appears to be in good condition, though I wasn't able to remove it, and didn't want to hit it too hard. Is there a tool for this?
So basically, sometime in the life of the bike, the crank was either poorly installed or poorly maintained, came loose, got b0rked, and needs to be replaced.
Thanks for all your help and comments. A newbie appreciates.
-F