Cluster Woes

You didn't say if illumination or hi beam bulbs work. If the panel isn't grounded by the mounting screws to dash, none will work except park lamp. the bulb sockets have 2 tiny ears that hold them in place and against the circuit board. If a ear breaks off they wont work.
Oil sender wire is likely the only gray color wire in the engine bay. With the ignition switch is on you would see 12 volts coming through that bulb. Ground the wire and bulb comes on. And that sender can leak oil into the wrong part of it and die. Usually will leak oil to the outside of it when this happens too.