Pulled the head for a head gasket... slightly worried about the wet stain around the #3 glow plug hole, and puddle in the crown of the cylinder...
Cracked head? Anyone seen this before?

First glance suggests it is running rich/lack of air/tuned up/lots of cold start/short runs?

I have two 200, and when I have had the glow plugs out at least one of them is covered in black oil.
I just consider it normal for an old cold running diesel.
One has visible cracks in the cyl head, does not use any fluids/pressurise etc.

Thanks Lynall. Still concerned with the puddle of fluid in the crown of the piston - something is leaking into there. Yeah, second car used on the island of Corfu, no motorways or fast roads here! Short runs everywhere, and only occasional use. Great machine for the off road olive groves though...

I think you will find the gap around the glow plug tip is the perfect place for any liquids generated during combustion to gather, why I have no idea?

Is the engine running at proper temperature?
I always found mine took pretty much 5 miles for the stat to fully open, 3 of them miles at 30mph then the next 2 miles at 50mph, then I could see the capilliary temp gauge climb a little higher than normal, then drop as the stat opened.
Winter was not good, as soon as the engine came off load (2 mile downhill section) the thing would start to cool down.

I've decided that seeing as I'm this far in, it's going off for a crack test - kind of seems daft not to bother.

Thanks for your replies Lynall