Nick,
from the photo it certainly does appear you have cracks which should not be there, but can you give us another photo not quite as close up so we can get a good idea of the area is that appears to be cracks.
To have a valve guide push out you most certainly have had a reasonably serious malfunction in an engine that is usually quite reliable, so a couple more photos would be helpful.
Beech.
Thanks,
What sorts of shots are you looking for? The outsides, the cylinder and everything else seems OK.
