You have a leak in your oil pressure guage, or in the line going to it.
Oil is actually pumped to this guage thru a small hard line to the oil pressure guage. The connection could have been cross-threaded long ago (most likely), or the line could have been crimped and broken (possible, but not as likely), or the guage itself is broken and leaking. Your insulation panel has probably been dripped-on for a long time, and now is overflowing into your floor. There's probably a big mess behind the dash below your guages.
You can access the back of the guages by carefully pulling the whole instrument cluster towards you. They are pretty delicate, with lots of wiring and such, so if you aren't confident that you can repair and replace it yourself, take it to a good shop.
A WARNING: Do not EVER start the engine with the oil guage disconnected, or you will pump oil all over the place and have a VERY BIG mess.
Hope this helps....