Steve
One signigificant factor in using the PSS system is that if you do NOT have a water feed tube to it, then when you haul the boat water will drain from it. Now when you launch the boat, there is an air pocket inside the PSS bellows. You HAVE to compress it by hand to "burp it" in order to let the water out. If you dont, you can burn it up.
They took care of this in recent years by adding the optional water feed tube to the top of the bellows. In 2007 when I replaced mine, I chose the water feed tube. Its not required for slow trawlers like ours, but I didnt want to have to remember to burp it.
In 2007 when we surveyed and then bought our boat, our PSS was never burped. I dont think the owner knew it was supposed to. The rotor had rust on it and it leaked slightly when the shaft turned. It was bone dry at rest. So I replaced it.
People ask how long do they last? Mine lasted 4000 engine hours and about 7 years.
Before I replaced mine I spoke with Dan Schalk, the lead engineer for the PSS system at PYI. He suggested that I take some fine wet sand paper and try to resurface the face of the bellows as was already described below. However, I found that when I tried to insert the paper, the incoming water pressure made it very difficult. It was messy. So I simply deceided it was time to replace it.
Its been very good ever since.
You can see my PSS installation with the water tube to it here
http://tinyurl.com/2e9ou5y
which is an article I wrote that has some pictures that show the PSS.
R.