I came here for an experienced opinion, my first mistake quite possibly.
Actually FieroWilliam, I’ll say that I’ve been on lots of auto boards. For quality of expertise this board is hands down the best. Hang around here for a few days and get to know the what goes on here. If you did, you’d have presented your initial post differently. You would have explained that you have a shop to do all of the actual refrigerant servicing but that you are doing the prep work.
I you hung around you’d see all sorts of crazy people trying to do things that they shouldn’t do - dangerous things. Unwise things. Self-defeating things. And even illegal things. On the face of it, your initial post gives no one any way to distinguish you from the daily stream of wackos with poor judgment and no knowledge.
So re-read the posts knowing something a little about this “place” - and then I think you’ll have a better understanding of where people are coming from. I absolutely did not miss the key question. People here try to give responsible advice - as in not helping people do bad (by whatever definition) things. Try some home HVAC boards. You’ll see that a lot of them have a strict “no DIY advice” policy. With good reason.
My A/C shop guy runs R12, btw - for exactly the reasons you gave. (Of course, he’s about 80 and spent most of his life working with/on R12 systems).