I had mine converted about 4 or 5 years ago because the manafold went. The dealer only works on 134a (i think that is what it is called)

I did not notice much of a difference -- The SL has a small interior and the system is more than able to cope with it.

I often use the ac when the top is down -- in the city, stop and go. I do not think it gets the cold cold that it did with the r12. But it is up to the task