Put a flat blade screwdriver under the screw head slightly prying up as you try to unscrew it.
Sure sounds like someone has been in there before for some reason.

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1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."