Tecumseh compressor shaft seal

Im trying to get my AC going for this terrible Summer that is upon us. I know the system blows cold when it has freon, but it leaks. I know i need a new shaft seal since i can see oil on the underside of the hood.

Question is, how do i know which shaft seal i need. I have the original cast iron Tecumseh compressor in the car (1968 j code with factory AC). Ive seen a few different versions of the seal for sale online. IDK if i need a late or early model. Any help pointing me in the right direction would be appreciated. Some install instructions or a diagram for the correct order of parts would be nice too lol.

The right way to do it would be to remove the compressor and have it rebuilt that way all of the seals are replaced at one time and you will only have to replace the Freon charge once, especially if you are using R12.