I'm keen to know this one as well. Mine has started to weep there.
Unfortunately this is a weakness of the A6 compressor. Every car I have owned with the A6 compressor has leaked from the shaft seal. I have never tried replacing the shaft seal but rather, replacing the compressor. The replacement A6 compressors will go for a year or 2 and then leak from the shaft seal. I never had an A6 fail on me but I hated the oily mess under the hood. It was difficult to keep the engine bay clean. There is a drop-in replacement for the A6 that is half the weight and half the drag and does not have the bad shaft seal design. It uses the same mounting, belt, & hoses. I think there are a few different brands. Here is the one I chose. https://www.apairinc.com/shopping/productDetails.aspx?i=134166. I liked it because it is black & has a larger pulley with a dust cover. To my surprise, when I received it.it was natural aluminum, not black.I called and asked about that and was told that the black ones are no longer available. I painted it myself and it turned out good. It works very well and I'm happy to no longer have oil slung all over the engine bay. You can try changing out your shaft seal but I believe it will just leak again in a short while from my personal experience. I live in central Texas where it gets very hot in the Summer so for me this upgrade was more important than originality. Here are pictures from my upgrade:
Actually, it depends on the refrigerant/ oil being used. I use 12 in my cars, with mineral oil. They don't leak a ounce, and I have never replaced a seal or compressor. I have seen the front seals leak across all manufacturers' compressor after retrofit to R134A w/Ester oil or PAG. I don't know the science why, it may be a smaller molecule, or maybe the Ester/Pag hardens the seal rubber, but I know my family has owned a 66 with the same A6 since 1986 and I've only recharged it when I changed a leaking Evaporator. It's been extremely dependable with its original refrigerant charge.
I think i heard, some gases will eat the seals over time.
I might have to upgrade to a newer style compressor.
they are all filled with R134a but with mineral oil? Or do they still run all with R12? R12 is absolutely impossible to get or refilled here in Germany.
I have r12 in all of my cadillacs (2) 1966 and (1) 1964. I got a 30 pound container of it years ago, and I still have some leftover. It's not even available in the USA anymore, but there is still old stock floating around for a price.
Lucky boy :)
We haven't R12 in Australia for ages now.
Three years ago I gassed up on R437A, that's now gone and R413A is the next one and its hard to get now. I think i'm going to end up with R134A when I change the compressor later in the year. But, I have got 6 degrees Celsius at the vents at the moment.
Regarding 134A when that might happen
Do you know about the after market part that when added in will control the evaporated valve to produce the correct pressures with that Freon and cycle the compressor on and off ( more efficient use of compressor ) ) in our stock systems when using the 134A Freon in our AC system ?
Enjoy and Stay Safe
Never heard of it!
I did a lot of research when I decided to upgrade my compressor. I have had other cars with A6 compressors in the past that leaked oil from the shaft seal running R12 and mineral oil. My research showed it was a common problem and there is supposedly an upgraded shaft seal that helps http://www.v8buick.com/index.php?threads/a6-compressor-shaft-seal-r.... The seal is available if you want to try it. https://www.ebay.com/itm/AC-GM-Compressor-Lip-Shaft-Seal-R4-V5-HD6-...
I just decided that I wanted the benefits of a modern compressor (less weight, less drag, designed for R134a, etc) and it is a drop in replacement for the A6.
The part Tony mentioned is called an STV eliminator kit which converts to system to a clutch cycling system https://www.oldairproducts.com/product/50-2503-stv-eliminator-kit.
I did not install the STV eliminator kit on my car. I was getting very good performance after converting the system to R134a with the A6 compressor but got tired of the oily mess from the shaft seal.
Now with the new compressor (10PA20HD) I'm getting great performance and no oily mess. One other addition I made for the upgrade is to install a pusher fan in front of the condenser. This helps lower the pressure on the high side. Another option is to install a high density condenser.
To Mark's point, the system was designed for R12. Life is simpler if you have access to R12. If you don't, the system can be converted if you take the proper steps.
TA-Motor is recommending a recharge-kit from Duracool. I was planning to buy a kit and a new drier/accumulator and try it on my car. But now when reading about the leaking compressor I think that would be a waste of money. Guess the best plan of action is to replace the compressor and drier and then have the system vacuum tested before refilling with whatever is available.
Another supplier for parts in Europe is Hansen Racing. Seems a bit cheaper when comparing to TA.