I started using this on all my cars a few years ago, and have been very pleased. It cools better than r-134a, and costs less. They also have a product called Proseal that will seal leaks in the metal parts of the system. Before I converted, I had a small leak "somewhere" that required me to top off the r-134a about once a week (no budget for a rebuild). After I put in the Proseal I haven't had to top it off in over a year.

Watch on ebay, once-in-awhile you'll real deals on the stuff.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire