Your car is a little new for my experience, but I have to ask - what size were these hex screws?
Judging from both of my somewhat older V-8s, there should only be four 10mm bolts holding the valve cover down. You didn't by chance pull the head bolts, did you?
Again, Not sure if things changed that much since '86, but 9 bolts along the top fo the valve cover seems somewhat excessive.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.