355 Common AC refrigerant leak points?

I would start at the hose fittings on the A/C compressor. They get disconnected for engine out services and sometimes the new o-rings don't seat perfectly when reconnected. Also check around the nose of the compressor behind the clutch for oil wetness which would indicate a bad shaft seal on the compressor. Of course the rest of the entire system is old now and an o-ring at any connection could have failed so a visual inspection of all the fittings looking for refrigerant oil/dirt stains would be next. If they all look dry and clean, add some refrigerant dye to the system and enough refrigerant so you can run the A/C again and inspect everything for a dye leak. Slow A/C leaks can be hard to find but if you are only getting a few days on a charge before the A/C stops working you have a pretty substantial leak somewhere and it should be fairly easy to pinpoint.

 

My car leaked at the compressor seal. I used this Harbor Freight detector to find the leak and replaced both the compressor and the drier. AC works very well now.

https://www.harborfreight.com/electronic-freon-and-halogen-leak-detector-92514.html

 

Don't fight it. Take it to a AC shop. They can sniff out the leak in 15 minutes with their sensors.

 

Indeed, I would gladly have had someone else take care of my leaking compressor but all of the local reputable shops were backed up 3+ weeks. The summer is short and sometimes doing it yourself gets you back on the road more quickly.

 

The compressors leak like a sieve.

 

I replaced my original leaking Sanden AC compressor and dryer a few weeks ago, links below from Ricambi America, (Thank you Daniel), I’ve included a diagram that I created with a listing of tools needed and compressor mounting. When I pulled a vacuum to monitor for leaks, I let my vacuum sit overnight.
https://www.ricambiamerica.com/157355-compressor-a-c.html
https://www.ricambiamerica.com/63934300-a-c-receiver-dryer.html

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It's also a good idea to check the condition of the radiator fans. The AC Condenser coil is located on the left side in front of one of the engine water radiators. I found that my left fan had blown a 30 amp fuse earlier in the year.
I had no indication as vehicle operating temperatures were normal. As the fans age, current draw can become higher. If this fan isn't running (normally cycles) the AC system will not recover and run properly for any length of time and proper charging of the system will not be possible.
Spal Fan 30102049 (30102050) NLA.
Lowest price I found was from Comfort Auto $135.34 with free shipping, Amazon.

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Considering you're going to spend money on refrigerant, compressor oil and a drier I think you'd want to take the time to replace the entire 25+ year old compressor and have one less thing to fail. Rebuilding the compressor might only cost $100 but I figured I'd rather replace it than have to deal with it in the near future and have a bearing fail or some other part fail next.