[Dukedesmo]

Looks like oil in the cylinder to make that much carbon. I assume not for many miles as the pistons look clean?

If I read it properly, it's the front cylinder that's oily and the rings & bores seem to be OK, correct?

Is it possible that the oil feed from engine to cylinder to head is somehow leaking into the cylinder? or even the head to engine oil returns? though you'd expect those to leak outwards.

I never did like the oil feed from engine to cylinder base hole on the front cylinder that has no 'O' ring, relying solely on the shim/gasket and any threebond/goop to seal it - though if it leaked it shouldn't get into the engine, more likely run down the side of the bike (plus mine have never leaked - and they've been apart many times!).

No cracks in cylinder or head? and what are the valve guides like with respect to wear, especially the exhaust side?

I know you were looking at guide seals but even if not good I wouldn't expect that much oil (my old Guzzi has no valve guide seals and doesn't use any noticeable amount of oil) although, consider the front exhaust valve/guide sits in a pool of oil so a leak on that one could be more of a problem.