That's a weird one and without having the bike right in front of me, I may not be able to give you an answer.

I've actually never had any trouble with my Sugino 103mm BB - or even various Shimano UN54 BBs ( which are considered by many as "cheap") - so it's hard to say. The only thing I can think of off the top of my melon is that the mismatched crank arms have different Q-factors and it's putting some kind of strain on one side of your BB. Either that or your BB shell was never faced properly and the BB spindle isn't sitting in there perfectly straight with the BB installled. I would probably start by chasing the BB shell.

Because I've never had issues with "cheapo" BBs (except the damn GXP that came with my Omniums), I don't really have an opinion of why pricey BBs are better.