I have a Milwaukee close quarter drill and use it as a sander,two years ago my son used it to do some sanding on a threshold, he had stopped using iras he said it made some funny noise.
As I had read about the failures with these drills I assumed it was history, anyway, I opened it up and found the rear bearing ceased, there was sanding dust in the housing even though I would blow it out occasionally.
So when the bearing ceased it rotated in the plastic housing and it melted/wore the opening, and then the armature would start to bounce around, making the funny noise.
I examined the bearing, it was a shielded bearing, good enough for drilling what it was designed for, but with sanding dust had gotten into the bearing as I found when taking the shields off.
So nothing to loose I decided to see if I could repair the housing opening, I got some two part epoxy (3M) and build the opening up, I had put the bearing back onto the armature and laid the bearing into the epoxy, closed the two halves almost tight and let the epoxy harden up.
Next day opened the drill up again and removed the armature and the bearing from it, cut the excess epoxy away, got a new bearing and reassembled the drill, plugged it in and pulled the trigger................... and she was just smoothly running again .
So the problem is that the shielded bearing will eventually get enough wood dust in it and cease up, and then ruin the housing, if this had been a sealed bearing this would not happen for a long time.
Mine is running again just fine, but if I ever need to buy a new one again (not likely), I will replace that shielded bearing with a sealed one right away.