So after spending an hour yesterday cleaning the cassette (maybe it was forty minutes), I would up with a chain slip and had to put on a new one anyway. Grump, grump, grump. Good thing I keep parts like that in stock.
Time to get a new one. If I can think of enough things to make an online order, I'll get it from Jenson; if not, I'll drop in at Kim's. (I should probably just get it at Kim's. They're probably starting to slow down for the season...)