follow-up: took car to dealer, replaced "klima" relay (climate control relay switch) and added freon with dye to identify source of leak. A/C works fine; will take it back after 1k miles so they can look at the system with an ultraviolet light to spot the leak.

The dealer is MB of Alexandria (Virginia), which is an offspring of American Service Center of Arlington, which also has a good rep. Have now received good service twice at MB of Alexandria.

JoeB