1990 Oldsmobile 88 Keep or Sell

I own a 1990 Oldsmobile 88 with about 54,000 miles on it. I bought the car six months ago from the original elderly owner for $1600. I bought the car as a second car especially for the summer because my primary car, a 1995 Acura Legend doesn’t have the coldest A/C system (and yes it’s been checked for leaks-none found-and freon topped off). So far I have spent about $700 on a new windshield, tinted windows and repairing the original factory CD player–all issues that needed attention when I bought the Oldsmobile. I was attracted to the Oldsmobile because it had a brand new R134 A/C system and a new remanufactured transmission installed both in the last few thousand miles. I had good luck before the Olds with a 1988 Buick LeSabre bought with the same miles and drove for 4 yrs that was senior owned, had an ice cold R12 a/c system that would freeze you out so I decided to stick with the same body style and engine (3.8 liter V6). The Olds A/C is ice cold too but the car only gets 15mpg in city driving and 19mpg on the highway. The Buick got 22 in town and 28 on the highway. The Olds will also need new tires and driver’s side power window work soon. I don’t want to spend too much more because then it might come down to the point of diminishing returns. I’m basically after a reliable low mileage sub $3000 car with an ice cold A/C system. I’ve read that R134 A/C systems in most cars after about 5 years have high failure rates because they run at a higher pressure and are not as cold as the old R12. Should I stick to cars with the old R12 system or ones with brand new a/c systems installed? What do you all think I should do with the Olds. Thanks in advance for your advice/opinions.

About all I can suggest on the Olds as to the mileage problem is verify the tune-up items are good, tire pressure is up, etc.
One thing that can hurt mileage is a partially clogged catalytic converter.
This can be tested with a vacuum gauge.

JMHO, but there are a lot of old wives tales floating around about R134. Higher pressures leading to early failure, 134 not as efficient as R12, 134 eats hoses and rubber O-rings, etc. are some of them.

Properly done a 134 system is fine, will get ice cold, and stay that way.
R134 is molecularly smaller than R12 so if you have a leak the 134 will have a tendency to leak faster than R12.
The obvious fix is to repair the leak and stop the bleeding.

Thanks for the info