Even using glass cleaner will make it sticky.

I bought a "perfect condition" 9400 a few years ago. Well apparently the seller sent me the wrong one, because the one that I received looked like it came from the ocean. Due to the sand all over the place, even the chrome wheel would not spin. When I took it apart, there were sand all over the place.

After many hours of cleaning it, inside and out. It started to work great. Here it is a few year later and I run into problems every several months. So I have to take it apart again.

Nevertheless, the back was sticky at first. Though I used denatured alcohol, something YOU do NOT want to use. As it stripped the paint off, so I am down to the bare plastic. As long as it functions, I don't care myself.

KOT