The oil in auto refrigeration pumps is easily fouled by the damp air from milkers. This air compressor from Harbor Freight:
Runs at 1720 rpm and has a valve body that can be reversed to make a vacuum pump with sufficient cfm to run a single bucket milker. There are other modifications; pulling the plug in he check valve, a vacuum regulator, a vacuum guage, etc., that need to be done.
I built milkers using this conversion for a couple of years. It's sufficient for milking a few goats morning and night. My problem was, people were using them to milk 100 or more and it just won't stand up to that. Not changing the oil in the crankcase on a regular basis and not cleaning the manifold of milk solids were other problems. A couple of years ago, you could buy a fine Surge bucket with a good pulsator on Ebay for $40. Those days are gone.
If there is sufficient interest, after we get back from vacation, I'll do a pdf of instructions to convert a compressor to a vacuum pump and if I have enough components left, to put together a Surge bucket for milking goats. DeLaval buckets that use a claw are better for cattle unless you don't mind applying inflations one at a time. They're more expensive though, and there are no rebuilding kits for the original DeLaval pulsators.
I'll sell instructions, including parts sources, milking instructions and clean up for $38 or build you a vacuum pump $399, you pay freight. I'll no longer put together buckets, just too much of a pain trying to gather parts since they're onto us at Ebay, but the directions would include putting together your own. That way you can build your milker as you can afford it rather than laying out the $$ all at once.