R-134 conversion

[batmmannn]

I have 3 cans of r12 in my garage left over from years ago. Here is my problem. My compressor is seized, so I bought one of ebay the guy swears is good but it has already been converted to 134a. He shipped it open nothing to keep the oil in it and the R12 nipple with 134a adapter snapped off leaving me a problem. OK I can take the plate off my old seized one and use it to get the nipple back in shape but the compressor oil leaked out all over the package the compressor was shipped in.

I don't know how much oil to put back in the compressor cause I can't pour it out and measure it. I suppose I could measure the oil out of my seized one and try this amount. Also I want to do this myself, so I am hinging on sticking with the R12 and 3 cans I have and doing a leak down vacuum test before I add R12. I can convert later if and when needed.

Now, my system is R12 and all the components, the compressor I just got was using r134a the seller says worked great when removed. He removed it cause he put a V8 in his car.

Obviously I don't know if he ever changed the oil. It appears to be green in color in the compressor I just got.

What do I use to clean the compressor and do I use mineral oil if I stay with R12 and also if I evacuate the system is that the same as flushing it? I really don't want a lot of expense.

Tips would be appreciated. Thanks