I don't have a manual on the MD11 but I just had a low oil pressure on my
new (40 hrs) MD2B and it turned out to be because the oil screen fitting
wasn't tightened down. On my model engiine the dip stick goes through the
large square nut that hold the oil screen down into to it's seats.

Appearently, over time, while unscrewing the dip stick, Ihad turned the
screen hold down nut enough to cause it to loose its seal..

I later found an old service bulletin reminding owners to check this if they
loose oil pressure (or reminding them to keep this nut tight or risk
loosing oil pump pressure).

Just a thought, FWIW.

Steve
s/v Good Intentions