1991 Oldsmobile Regency what type coolant is correct

It take's the green coolant they put the right stuff in. It's possible that coolant exchanger could have broke loose something floating around in the cooling system that was plugging a leak.I don't know all the most common point's of leakage on that engine. But what I suggest you do is rent a cooling system pressure tester they rent them at auto zone and pressure tester your cooling system and find all the leak's that way. Also pressure test your radiator cap you could be loosing coolant that way too. Read the pressure on the cap and pump it up to that pressure it should hold the pressure on the cap if it doesn't then replace the cap.