This lens is one of the best and easiest to dis-assemble for cleaning. I've gotten 2 for cheap and cleaned them as well as my 3rd one. Great lens, perhaps maybe not as good on extra large prints 16x20+ but still excellent for the money.
The front and rear groups come out easy, thats the first step, if you clean those surfaces and that does it then Stop and put it back together. Let me know if you need to go further.