Hi Mark, I think you are giving the Robustness of the corrector plate a bit of a bum rap.
I have had a Schmidt Cassegrain for over twenty years and cleaned it many times, without a mark on it.
I suggest that you get in touch with "BinTel" and get a bottle of their lens and plate cleaner, it works wonders.
I saw it demonstrated at AstroFest by Don Whitman a few years ago and it was just fantastic.
Slight smears on corrector plates do not degrade the image one bit.
The Schmidt 48" plate at Siding Spring get cleaned with Windex.
They get bird **** and other crap on ,and it has been working for over thirty years.
Cheers
