Mike ...Thanks for your post
Guess what. I just found out from your post that I was a victim for those fake R12 cans. I bought 4 cans on ebay for about $84 and they are exactly what you described; white cans with R12 in red and the back has prints in spanish. The top of the can looks exactly like the R134a cans. The A/C in my BMW was working like a charm two summers ago. Last summer It wasn't cooling enough. I checked the charge (DIY-I am cetified for all A/C systems). It was low. I got the cans after 1.5 months and the S.O.B left me a negative feedback (the only one) when I asked for my money. I added 2 cans but my system wasn't cool like it was that summer. I took the car to a my friend's shop and he evacuated the system. I took the drier out and it was rusted. Got a new one and took the condenser and evaporator out. Flushed the whole system and then decided to get a new compressor (maybe it's week). I got one for $125 on ebay. When I tried to put it up, I found that the mounting points are different from the one I have. I had to leave the old one in the car. Put a new expansion valve, high pressure switch, and fresh oil and used the same Mexican cans and still not cool enough toped with a real R12 can. I checked every single electronic A/C part and they were all fine.
I said F*%K it, and sweated my ass off all last summer. Now I know what I have in my lines.
Man I am mad at that guy and I will report him to ebay.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer