I thank you ALL for the help. I don't have the wrenches I need. So before buying them and trying the job of replacement, I think I will try to remove the end and fit a new o ring. This is no easy task. Very good possibility I will not be able to reassemble in place. But the most I can do is ruin the valve.

It is strange that the replacement valve did not ask which gas was in the system. I went to several suppliers on line. Be that the case then instructions on adjustment should accompany valve. ( One would think)

I was also torn with the thought of retrofitting to r134a as long as I am faced with replacing the Valve. But I have certainly read enough articles about trouble that exists with retrofit. I know on a personal level, at work we had many leaks develope after retrofit. Two reasons were named. one was the fact that the oil is a great cleaner, the other was that the mixing of the two oils caused a reaction on the o rings. This proved somewat true in newer intalls with same gas. No leaks occurred at all for years.
Well,
Thanks again,
Ron

__________________
I love my Mercedes