I was planning on using Bg Frigiquiet Universal oil in my r12 A/C system. But, after reading the technical data, it is only "recommended as a top-off lubricant" in r12 systems.
http://www.bgimw.com/AC2008/ACtech.html

I don't know what oil was used in the compressor when it was converted to r-134a because I don't have the records for the conversion. Just a compressor which was new in 2000, and a fitting on the A/C low side. Installing a new r4 compressor this weekend, after a good flushing and replacing the drier/txvalve, and refilling with r12.

Would Mineral Oil, 500-525 Viscosity be the right oil to pick? I assume I can get this from a Ford, GM, etc dealer or a chain auto parts store? Time is running out for ordering online because I'm doing the job on Sunday. Or would some other synthetic oil work, like an Ester POE?

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1980 240d
1999 SL500