Yesterday when I started my 1988 GXL up, the oil pressure did not register on the gauge. It was flatlined, so I opened up the hood to see if there was oil pumping through the system. It started leaking at the base of the gauge where it threads in, but only when the car was running. As soon as the engine was turned off, it stopped leaking. Obviously, the oil pump is doing its job, so I decided that I will need to purchase a new gauge.
So, when I started the car again, the oil pressure gauge is reading fine. I actually drove about 250 miles yesterday after this problem and that gauge was perfect all day, with no leaks at all, and oil level fine.
WHY did it leak only for a little bit, then not anymore after the car was re-started?
AND do I have to replace the gauge itself, or is there also another electrical problem coming into play here? If anyone has info or advice on what to do, it would be greatly appreciated.

Thanks