82 GPZ 550 Loss of oil pressure after a drop

Oil pressure gauge arrived yesterday.
Today i've tested oil pressure and the readings are fine. Cold oil - about 2500 rpm - 50 PSI. So, the oil pump works OK (good news).
All the time, during the test, the warning light was ON. This time it did't even went OFF after start and just to came ON again after a minute. It just stayed ON.
Before that, I've left the bike on the side stand for over 3 days and I've noticed something. Fresh oil is black and full of coal-like, soft, fine, junk.
The bike has been sitting for past 10 years.
The joke is on me. I've just used MOTUL 300 V to flush the engine.
I think that it is imperative that I remove the oil pan, clean it, change the oil and oil filter and clean the sensor (soak it in brake cleaning fluid or something like that).
The problem is: where am I going to purchase oil pan gasket for that bike during this corona-shit time? If I remove oil pan on that bike I know what would the gasket look like.
I'm located in Europe.

And, Thank You All. You are great! Ride on!!!

martin_csr wrote: Bypassing the oil level sensor should be pretty easy. It only has 1 wire w a male bullet terminal, so as a test, you could disconnect it & secure the sensor wire so that it doesn't get damaged. If the oil warning light is still acting up, then the problem is the wiring or the fuel gauge / warner unit. If the oil light returns to normal, then the problem is the oil level sensor. I guess this is correct or pretty close. hee.

You are on to something. The fuel gauge also acts silly. I have a gallon of fuel in the tank and it still reads empty. I've fucke'd up when I was reparing the petcock.

You could cut your own oil pan gasket, assuming you can find some suitable gasket material in your area. To make the bolt holes some sort of sharp punch works well.

Oil level warning light is OFF now.
I've removed and cleaned the sender.
But, oil level in a revision shaft has to be higher than MAX.
With the engine running, the oil level drops to just above MIN. Then the light stays OFF.

I don't know what to think about that.

I have a 82 Spectre motor (750) converted to chain drive and mounted in a kz650 frame.
It had one of those oil level sensors on it but I did not want to use it so I took it apart. It has a float inside it shaped like a donut and is rides on a shaft, when the oil level is low it grounds out one half of the switch. I noticed quite a bit of oil sludge inside the can the float runs up and down in, so there is a good possibility the sludge could make the float "hang up" cause the oil light to stay lit. I ended up putting a regular oil pressure switch on the end fitting that the oil pan has.