Odometer/Speedometer

These PRE CAN BUS vehicles have a large number of connections and usually several multi pin connectors attached to them. At this point in its life, corrosion may be an issue at these connections. It is a hassle to get the instrument cluster out but it can be done, instructions here: https://www.youtube.com/watch?v=OZxOYXNm_t4 The maker of this video would be good people to speak to about this issue. I am certain they have seen it a thousand times

Im reasonably certain the odo/speedo situation is one matter,and the oil light another. The oil issue can be SERIOUS. 1 Check to make sure you have enough oil. 2 check for any obvious leaks.(oil sendind switch) 3 If the car is making noise when the oil light is on "clacking" get a pro to check it out- quickly. 4 remove your cluster,check and clean connections.If you have a speedometer cable(not an electronic cluster) make sure the cable is good at both ends,lubricated,and the inner cable can turn.If not get a used cluster.Careful with the mileage!

Is the dash cluster mechanical or digital?

Mechanical

I would check the VSS (Speed Sensor).

Otherwise cable is bad or gauge itself.