Maybe they've changed it, but on my '85, I've got two studs/nuts on opposite sides that hold the oil filter cover in place.
BTW, on my car, I get about 1.5 bars at hot idle...maybe down to 1.25 bars after a long run...also, for those who mentioned cleaning the sending unit terminals, as far as I know, all 123 cars use a purely mechanical gauge, although the 126 cars use a sending unit/electrical wire...
Also, my truck shows 10 psi on the aftermarket mechanical gauge, and runs fine...so I wouldn't be worried.
