This is the cause for a lot of oil leakage on m42's from the front profile gasket. In the Bentley it tells you to put two screwdrivers into the camshafts and pry down and then tighten the bolts. Notice the bolts for the upper timing cover are not completely threaded and the covers holes have a slight oval to allow for this.
I actually just put my timing cover on today with all new profile gaskets, etc etc. And I was surprised to have the same problem, since I know it sat flush before I took it apart. I ended up using some clamps to press the cover down and sandwich the new gasket better. There is still a small lip there though.
For some reason it didn't even occur to me to use the camshaft trick (since my e30 Bentley has no m42 info, I've been winging it mostly). But now I will to get that extra tiny bit I need....
EDIT: worked great. Make sure to put a pad or towel or something between the screwdriver and the top of the timing cover, so as not to scuff it up or mar the surface. I used some old sparco harness pads
