Well, lucky for me I have a bike co-op in town with tons of partner-less left crankarms, I'll grab one and see if it solves the problem- the matching thing isn't really a problem, this is a no-budget beater commuter bike. If that doesn't solve the problem, I'll invest in a new BB and chuck the junk crankarms and no one will care or remember them.
Thanks for the advice, all!