Okay just picked up the new noted orings (FRONT), WOW they are larger then the ones sent with the A/C compressor by Spectra Premium (BACK).

https://i.imgur.com/4WGSGdT.jpg

Why doesn't the manufacturer SEND the proper orings for the make/model of the car? One has to do such extensive research and forum hunting to find these two proper seals for the R4 compressor for the W123. I can't imagine how many shops, people are probably using the incorrect one.

I doubt anybody here knows "all brands" and variations of R4 compressor out there. Best to measure the depth of the recesses. I gave above the dimensions for a new R4 I put in my 1985 300D.

Personally, I prefer the O-ring groove type, since O-rings aren't a treasure hunt. When I got a few sealing washers from NAPA, it was the only box on the shelf and had been sitting there for decades, so the next guy will get "not avail".

If an AC shop is doing the job, and dumping this search on you, I would question their professionalism. The R4 was used in a gazillion GM vehicles, so they should know all about them.

The front ones do look larger than the back ones, but that is to be expected in a photo. Seriously, what dimensions are larger? O.d. i.d. ?

Dimensions for seals are listed in post #8.

The recessed port compressors are the same. It's the hose blocks that are different from one vehicle to the next. The W123 hose block was not designed for the recessed port configuration to start with. In my experience, getting a leak-free seal with the recessed port compressor is a challenge. Much more so than with the original o-ring design.

Pretty much true for repairing or re-designing anything on all cars. Most people are too lazy so trust a "professional", but that often doesn't work out because they can't afford to do the research. Most of my relatives go thru cars like you wouldn't believe, usually trading one problem for another. Being an engineer, I am used to digging thru drawings and specs and double-checking everything. If not, things like the Apollo 13 incident happen - 12 VDC relay left after controls were upgraded to 24 VDC, overheated and blew up oxygen tank. At least your M-B stays grounded where failures are more benign. I usually verify parts against photos on rock's site, ebay, Google Images, and download catalogs from Gates, Goodyear, SKF, ... As you do find info, post it here for everyone, and smart people will file it away.