I had problems with broken individual cams and bushings in the attenuator of a 7A29, which I think are the same gray plastic. I had to do some tricky repairs to put them all back together. The story starts here and there are some nice pictures associated:
/g/TekScopes/message/206747In my case, the cams did not wear down or anything like that - they just broke open from around the shafts. The plastic was still shiny and had good surface, but simply cracked apart I think due to being too flimsy to take the stresses - those should have been stouter or of a stronger material. I also think the too-radical lift in the cam and follower design and lack of lubrication aggravated the situation, as described in the discussion and picture captions. OTOH, I also noted that the bushings are low stress items yet cracked anyway, so there's an aging/chemical deterioration issue too.
Ed
