Destroying cameras

I have done something quite stupid. I have an old beautiful Pentax SLR camera and some of the foam seal in front of the ground glass is perishing. I tried pulling the loose bits of this seal away and they fell on the ground glass, stupidly I tried cleaning it and have rubbed the foam into the ground glass. It is quite stuck in there and I don't know how the clean it off.
Before I wreck it anymore can someone give me some help?

When I look through the viewfinder it is all quite smeared and funny looking.

In an ideal world - as you've discovered - you shouldn't let the old foam come into contact with the focussing screen. However, now it's done you have nothing to lose in cleaning the screen.

I use lighter fluid and dab it on with a cotton bud. Rub the screen very, very gently with the bud and when you start seeing dirt build on the bud then change it for a new one - repeat as often as neccessary. Take your time and don't apply pressure, let the lighter fluid do the work. Whatever you do, don't touch the surface with anything sharp or it will scratch very easily and you won't be able to repair the screen. Don't overload the bud with fluid or it can drip down into other areas that you don't want it dripping into (although in reality it probably won't do much harm and will dry off quite quickly). Finally, it's worth mentioning once more; take your time!

You should find your screen's as clean as a whistle when you've finished - if there's still corroded foam in there then get it all out before you start cleaning otherwise it'll just drop onto the screen again and you'll be back to square one...

Good luck!

my Dad did the exact same thing with a Super A, we never could get it off no matter what we tried and ended up selling the camera for spares or repair.

best of luck

Old and rotten light seal foam is one of the hardest things to remove from any surface (it seems to take on the consistency of permanent marker ink the second it touches anything you don't want it to touch) - the trick is to keep persevering. Lighter fluid will do the trick eventually but don't be suprised if it takes hours rather than minutes. I don't know of a quicker way or a more effective cleaning solution but if anyone else does then I'm all ears...

but don't be tempted to use acetone, if you apply that to a plastic surface which is meant to be clear it will destroy it...