Harvey Yau , May 21, 2000; 11:58 p.m.
It isn't a pentaprism you need to be worried about, it is the focusing screen. I don't think the Rebel 2000 even has a prism, from what someone has told me, it has uses mirrors to accomplish the same effect.
Again, I'm not certain about the Rebel 2000, but I do know that you can pop out the focusing screen on an Elan IIe by using a pin to prick two metal loops near the lens mount on the focusing screen. I don't know if this is even possible with the R2k, but examine yours and get back to me. I'm going to disclaim all liability to anyone who attempts the below operation on their camera and messes up. Do this at your own risk.
On the Elan IIe/50e, which is not supposed to have a removable focusing screen, you can prick the two sheet metal loops inward. By doing this, you are disengaging a pressed sheet metal retaining plate. After this comes out, very gently use a pair of tweezers to remove the screen by the edges.
You can now clean the screen in whatever way you see fit. I use compressed air on the laser etched side (never touch it! you already did when you tried to clean it...) and my microfiber cloth on the smooth side.
Never *ever* touch the mirror! Don't let the focusing screen touch the mirror either.
Focusing screens can be replaced by calling Canon's parts department. They're inexpensive.
The more expensive the camera, the easier it is to pop out and exchange focusing screens. With my EOS 3 it is as simple as manipulating a little tab on the inside. The focusing screen comes down on its own little tray. New focusing screens for this camera come with tools that you should use to pick up and remove the screens.
Good luck, let me know how you make out.