It sounds like it could be the oil sump?
Have you checked this?
start by looking to the oil sump. Could be that the O ring is worn and its just a simple replacement.
I would personally suggest that given where the car has lived and its inevitable hard life. Start with an oil and filter change. That should eliminate some problems.
Sounds like a possibility, you probably need to replace the switch!
no worries, and at that price, even if its not the right part, its still a cheap update.
I would recommend ensuring that you have replacement seals for oil filter, and the switch.