Opened up the cover in the Primary Chaincase by the rotor so I could check the timing, and loads of extra oil came flooding out. I know the correct amount was in there, so where's the extra most likeley to have come from?
Oil has dropped from the main reservoir, but I have a leak anyway. The oil seemed quite thin. From the gearbox?
Also have great difficulty finding neutral gear when engine warmed up. Any suggestions?
Check the holes in the inner primary that allow the excess oil from the primary to drain back into the crankcase as it sounds like they are blocked. The engine and primary oil are shared on a T140 and the engine breathes out through the primary.
65 - Sounds as if your engine is trying to "oil wet sump", but the crank is throwing all the excess oil over into the primary case. Normally it would level out by draining back through the 3 small holes Kommando said to clean... then the oil pump would take it all back to the main oil tank.
You'll simply have to investigate. Do a search here on "oil wet sump". There's lots written about the subject.
Too much oil in the primary would make the bike very hard to shift. So I'm not convinced that your 2 issues aren't connected.