Coolant Leak help please

My first thought was that the overflow was blocked. Are you sure it's not become kinked somewhere? You shouldn't get pressure in the expansion tank at all really so something is amiss somewhere.

There is a 3 way thermostatic valve in the system, is that functioning correctly? It appears to be on the offside of the bike towards the bottom, looking at the diagram in the manual. Three pipes connected to it.

My guess would be that for some reason the coolant isn't circulating and too much heat is generating too much pressure causing it to blow back into the expansion tank which isn't designed to handle any pressure. What temperature was the engine running at? You'll have to watch that as you could seize the engine if it gets too hot while running.

I think I'd locate that thermstatic valve, take the bike for a short run to get it up to operating temperature and then feel all the coolant pipes. If the circulation isn't good you should find one that's either a lot cooler or a lot hotter than the rest. The blockage/fault is going to be near there.

It is common, nearly all mine have done it, it is only minimal and nothing to worry about, but keep your eye on it in case it is more than that:thumbup

Doesn't sound like you have too much of a problem there then mate, especially after Badger's comments above :thumbup