"very good original patina rider", that one's good!
Goldie-tank, Goldie-exhaust, Goldie-mudguard, siamese-pipes, that's not quite what I would call original. Just have a look at the RHS footrest and the gear change lever, then you know why he fitted all these new parts, incl. the handlebars and controls.
Nevertheless a nice bike with original engine, but I personally would not pay more than perhaps 3500-4000 USD for it.
OK, maybe a bit more if I had a chance of seeing and test riding it before. Although - in fact, all vehicles I ever bought have become cheaper after I saw and test rided them.