Look up the necessary ohms meter readings for that exact sensor and measure it to see if it is within top/ bottom limits.
You'll have to heave to if you are a one engine jobby though.
Fluctuations sound like possibly the sender / sensor unit as I have always found a worn rear main normally controlling the oil pressure depicts a constant low reading and only increases with applying more revs.and on tickover when hot brings on the warning light on the control panel.
Manual test kits with adaptors are cheap as chips nowadays but make sure you have the correct screwed adaptor in the kit.
Sender units are also cheap so sometimes you may feel that unless the kit comes in for other jobs it's not worth buying it and it's maybe better to get another sender.
Best of luck!
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.