From what the (non-techy) guy told me, definitely a valve problem, 2L - I'll know more once I speak to the mechanic.
Jim
Still not spoken to the mechanic, but I thought I'd peruse the workshop manuals for the touring bikes and the SE bikes for clues. Interestingly - if the manual(s) are correct, while the '07 touring bikes still have a "locking ring" - a circlip I guess - on the guide to prevent it from going downwards, the SE heads appear to have no such locking ring! So, if that is correct, are we sensible in guessing that the extreme rear head temps - remember our old friend
detonationum extremis as they used to say in Rome - meant that the alloy head and the (phosphor bronze???) guide, with their differential coefficients of expansion, expanded too differently and when the bike cooled overnight the guide dropped as it became loose.

We'll never know I guess, but I still find it more than a little surprising - if it is indeed true - that standard heads have the circlip on the guides, while Squealin' Beagle heads do not!
Jim