So the little plastic wrench that has a small "finger tight" torque spec and that forces the crank arm against the rubber bearing seal (the orange washer-like thing in the pic below, two of which came with my bike) is not suitable for AC preload, but rather is for radial deep groove bearing preload. I guess it should have been obvious: a thick elastomer washer is going to squeeze under the axial thrust generated by the radial force on the pedals and chainring. Although the bearings pictured below are claimed to be AC bearings by RWC!

dsaul, I think that this is what's happening: you graunch down on the pedal, which applies radial force to the bearing. The angular part converts this to axial thrust, compressing the seal. This eventually degrades the seal and gives you the symptoms you mention.

I guess I can pull my crank pretty easily and inspect, but what' I'd like to do is order the right part, and strip my bike (spring cleaning) of parts and wash it. Then reassemble with new bearings, cables, and tape. I think I'll pull the crank...

Thanks, guys!