I am a long time PST owner--got mine back in 2005--and I recently became aware that many PST's share some common problems that degrade the view they provide. Just about everybody knows about "rust" on the objective (the glass on the front of the scope)--mine developed rust in 2006. I shipped it back to the manufacturer for a fix and they shipped it back to me with a clear blue objective. No problems with that since. If you have a clear blue objective you are probably OK there, too.
However, the fix involved putting a filter at the base of the eyepiece barrel and these filters can degrade over time and get "rusty". The problem is, the filter is buried in the innards of the PST and many owners don't know it's there--I didn't. And it's not as easy to check as just looking at the objective but it's not that hard, either. It involves taking the side cover off of your PST.
The rust happens gradually and kind of creeps up on you. You can still see through the scope, but detail becomes less sharp--like when you're observing through poor transparency. People even think that's the cause--unaware that actually it could be the scope.
Anyway, the views with my PST were not as good as they used to be and when I stumbled across a couple of threads in this forum describing the problem (and the fix) I decided to investigate. Sure enough, my filter was rusty--not completely clouded over but covered with little splotches--which was enough to affect the view.
While checking the filter, I also found that my scope had another common problem--a misaligned pentaprism.
The fix for both these problems is relatively easy to do. I had to buy a couple of tools but they weren't expensive and hey--it's always nice to have a reason to buy new tools, right? My PST performs better now.
Here are some links to threads that have info, pics, and embedded links to more info and pics.
These are links for the replacement filter.
I passed on this information to a friend in Germany who was unhappy with his PST. He found that his scope had the problems, fixed it, and was rewarded with much better performance. He passed it along to a friend of his with the same happy results.
You will see if you read the above threads that DavidG provides much useful information and advice. He suggested I make this post to let others know about the problem and the fix. Dave helped me a lot and I thank him.