My experience repairing 400K drives is that they're tough little devices, but when they're dead, they're dead, unless you have a scope or something to work out what is wrong with the electronics. My regime is to clean off the gunk, re-lube with sewing machine oil, and don't go near the electronics or heads apart from removing dust. If it doesn't work from cleaning it up (and most do), chances are the heads are mal-aligned, gears are mashed up/worn out and stripping down the drive is beyond the point of repair to me.