Outer Limits 4x4 Board

I just replaced my glow plugs this morning and one of the old ones had heaps of oil on it when i pulled it out. What could be the cause of this and is it bad.

Sam

Either came through worn valve stem seals, or from worn piston rings.
How old/ many kays is the engine?

about 150 since last rebuild but i think if fried the rings last year and that may be the cause.