I'm at wit's end with this one... I just changed the spark plugs on my E320. I discovered that three of the six-long 5mm screws used to hold the rectangular cap to the valve cover weren't even tight. I figured the previous owner was lazy. I replaced all six-screws with new ones since they were rusty on top and the allen recesses were starting to round off.

I easily got the screws for coil #4 to screw in nicely. I only got one of the two screws on coil #6 to grab, and on coil #2, neither screw grabs. I removed the cover ten-times and tried refitting it - that didn't work. I made sure the three coils were down far enough into position, I made sure the spark plug wires were all in position. I even made sure the rubber piece that goes along the side of the valve cover (under this cap) was in line. I tried screwing the screws into their holes individually without the cap and they all screw in perfectly. It's as if the screws for coil #2 and #6 aren't long enough. I also removed that spongy thin rubber gasket that goes around the perimeter of the underside of the cap to buy me another 1/4 inch or so - no luck. Has anyone else experienced this?