[rdavisinva]

This may be a stupid question, but how would I know if this has happened? I took a look and gave it a good wiggle and it seemed to be firm, no movement at the fitting, so I think it's good?

Also, I happened to talk briefly to a large engine diesel mechanic, and after a very brief discription he mentioned it could be valves out of adjustment? It has been sounding a bit noisy... any thoughts?

Never heard of such a thing.
I don't think valves out of adjustment could cause oil to push out of the dipstick.

Blow by, overfilling the sump, and clogged crankcase breather are the only things I know of that would cause the oil loss through the dipstick tube.

Assume you are referring to the 12J 2.5 N/A 4 cylinder diesel, Steve.