Dremel 8100 cordless

Gentlemen- 
 After my third purchase of the same tool, (8100), ive become curious as to what I’m going to need to make this thing work properly. The first two I brought home I returned until the current and third one I kept and thought the problem was exclusive to the previous tools. But it’s not. The problem seems to be in either the speed controller, or electronics-I’m leaning towards the speed controller as it seems to do better when I give it a detailed cleaning. I have some experience with electronics so I choose to do the repairs myself. (I know this voids any warranty). My inquiry is about replacement parts- I would assume these are available thru a web site? And is there any reports of this issue and how to correct it? Thanks for any reply’s.