Those bikes are fun. I own an '87 XL600R I bought for 600 Euros which is essentially trouble-free, apart from a broken stator coil I had fixed. All PD03 do that sooner or later.
My friend's got a Xl500R PD02 pro-link he bought for 100,- that needed nothing more than a service. They like to weep oil from the head but don't bother, they all do that. Just wipe it off.
AFAIK the only proper forums are the german ones:
but don't be shy, ask questions. There are a lot of specialists and a german part supplier posting there (Erik from alttec-classics.de) and at least some of them write good english.