Hi Andy,
there's lots of information both here and elsewhere on the internet about how to maintain the La Pavoni lever machines, complete with photos diagrams and everything else you could imagine. You'll never feel alone
I'm afraid it is not normal for the double basket to be such a tight fit you cannot remove it from the portafilter.
Is there any evidence of the basket having been dinged around the rim which would cause it to pinch the portafilter?
I would also disgaree about the single basket, depending of course on your preference in beans/blends, taste profile, shot volume and so on. The La Pavoni can deliver a tremendous single ristretto and very nicely nuanced single normale, although you may find it takes a little more practice than the double basket.
One way or another you have a tremendous journey ahead of you with the Pavoni, which will just continue to surprise you - and you will find plenty of fellow travellers here with whom to compare you experiences and who are generous with their experience and advice.
Cheers
Mike
LMWDP No. 237