I had the Panny 28PL1 and had the dirty patches as well.
Also very recently the picture has started shaking - very strange indeed. Had the interference through any Scart - RGB, S-video or composite and even tried a friends scart lead (cost him £80

) and still had the interference and i'm sure pin 19 was disconnected.
Had to really drill it into Debenhams to get them to swap it for another tele but I think they saw the light when I asked them for a Loewe Xelos 32" instead. As soon as I mentioned this was what I wanted to replace it with they got more apologetic

The service company were about as helpful as a turd when I reported these problems and the engineer couldn't do a thing about it apart from offer to wave his magic degaussing wand - that'll fix convergence issues etc etc won't it
I had the TV for about 5 weeks by the way and Debenhams were very difficult to deal with, I didn't know about their 28 day refund policy thing either until after the 28 days were up of course. although we told the store during that time we had problems they just said we need an engineer to look at it even though I knew they wouldn't be able to fix it. We moved house during all this as well so it was a really hassle and I didn't need it at the time. But as I said they agreed to a swap in the end so it ended ok I just hope the Loewe doesn't have any problems. It took enough persuading my girlfriend we needed to spend another £400 on top of the price of the PL1