My refrigerant shows green in the sight glass because of the leak detection fluid added by my mechanic but the key is bubbles. More bubbles means less refrigerant. My '87 300D has a tiny leak (about 1 pound of refrigerant per year) in an expensive place to access, back by the firewall under the windshield wiper motor. I probably won't have it repaired unless it gets a lot worse.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970