I think you are wise to get your own tools and become an A/C "guru" with that many cars to do. Here's a source for knowledge and good suppliers. I recommmend either AC Source or AC Kits as a source of all you'll need. Phone calls to either will yield friendly help in equipping you.

http://www.aircondition.com/

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)