I have heard a lot of talk about using the "proper" green o-rings for r-134a.
When I went to do my system I found all kinds of different colors (blue,
green, and red)and they were all supposed to be good for r-134a.  If you
notice when you put a little oil on the o-rings (which you are supposed to do
before you install them) the coloring comes off and they are all black
underneath anyway.  So it is my opinion that they are all compatable with the
new stuff now and if the old ones weren't it is because they have absorbed
some of the old refrigerant oil not because of what they were made of.  I
could be wrong but even some of the literature I have gotten about doing the
switch says that on newer cars (newer than '78) it is not manditory to change
all the o-rings only the ones on the compressor (unless you have a leak
somewhere).  Let me know what you guys think about this.  I am always open to
learn new things.
Ken Wilford
John 3:16