welcome to the board.
first, i'm just curious as to how you've determined you're running rich? is the car modified at all?
second, i'd suggest getting a Factory Service Manual so you can check the wiring associated with the gauge. what you describe sounds more inline with a problem with the sender/gauge than an actual oil pressure problem. that said, how bad is this leak you mentioned? where exactly is it located? (your description is too vague).