MY car is 92 L98 gta. I have had the car 20+years. I was changing the oil and I noticed a oil leak. The car has never leaked anything as long as I have had it. I traced the leak to a sensor on the back of the AC comp. My question is what are the steps to replace the O-ring/seal under the snap ring. Also do I need to have the system recharged. The car is still running the R-12 in it and right now and still works fine. I don't want the system to get low and damage the comp. Thanks for any help.

 

That's not a "sensor"; it's the high-pressure safety cutoff switch.

Yes it is immersed in refrigerant. You will lose it all when you remove it.

Steps to replace its O-ring are, recover the refrigerant; remove the snap ring retaining the switch; exchange new O-ring for old; reinstall the switch; recharge the system.

If you have ONE leak in the AC system, others aren't far behind. I'd suggest that rather than going through all that with the O-ring, you replace the compressor, switch, accum/dryer, rubber lines, and orifice tube; and convert to R-134A. After having the R-12 professionally recovered. (one of the few times I'll ever recommend "take to shop", unless of course you have a recovery machine and a place to take the old stuff to)