To the original problem. On my 85 3ooSD ( new to me) the same problem when I would drive it kick the turbo a few times i would get home and the dipstick had popped up. I also noticed oil around the filler cap. I cleaned the filler cap seal and cleaned the dip stick. Then I had the EGR off and sprayed WD40 into the small orifice on the side. As this car was new to me I also added a Diesel fuel conditioner ( It was in the trunk unopened) to 1/2 a tank) and drove it at highway speeds for a few miles. I got back and no leaks , no runs, no errors.
I do not know what was causing it but it was gone.