Steve Brotherton (stevebfl) has posted on this, too, from time to time.

He believes it is a big mistake to convert from R12 to R134a, and there are a lot of reasons. If you search for all of the posts under his user name, you'll see all of the reasons why, one of which is that R12 is still the cheapest component of your a/c system.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".