Oil pressure gauge

Common failure in that generation are the driver motors for the gauges. What do the gauges do when you first turn the key on? Does the OP gauge stay pinned when off? If yes then it is likely a defective motor, there are multiple places who rebuild them or if you are good at soldering you can remove the cluster and DIY, but be sure you know your abilities as it is very easy to damage the board with excess heat.
If the gauge drops back when you turn off the key then you have a different issue, the wiring to the cluster has a short.