What could be the problem when my PT overheats and has an oil leak?

Hate to say but it maybe the headgasket. See if you can get a pressure ck done on the engine. Also does the fluid flow out of the reservoir? A leaking headgasket puts compressed air from the pistons into the water jacket. If you are good you can DIY it and save a ton of money. If you can and is driveable have Firestone or Goodyear ck it or get a shop that is good, ck with family or friends.

Also a stuck thermostat would be the issue as well. It is called boiling, that is when the coolant litterally boils and goes thru the reservior just like a leaking head gasket. I agree, stop in or call them first there maybe a charge and an appt needed to do the test. Ck with the parts stores as well, if they havae the pressure tester you can rent for free.