I had a small B&D plunge router which I bought second hand many years ago. Plastic construction so when that gave way I simply pop rivetted ally bits on. Anyway,recently it went bang so took it apart to find that one sealed bearing it had virtually seized up causing one segment to go out - oh,how I miss the growlers from work days! Just did a test meter check. Left bearing in penetrating oil for a couple of days - no change so bought another bearing, put it back together and it worked - for two minutes. I'd gotten (sorry,I spend a lot of time in Texas) so missed it, Bought an identical model for under £20 on EBay which was in it's box and like new! Sorry to go on but the of the morel of this story is to keep your sealed bearing lubricated. Oh, I had forgotten that I had left the old bearing in the penetrating oil for about a week and found it was as good as new - so there's another moral!