I just replaced the master cylinder on my 83 300TD. I noticed for the first time (I guess) the two black buttons on the top of the brake fluid reservoir. Each one seems to be associated with the level switch connectors on the front and back reservoir sections. Any idea what these two buttons are for? They each have a spring return function of some kind.
Thanks for your help.

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1983 M-B 300D, 148K, daughter's ride
1983 M-B 300TD, 120K, my ride
1985 M-B 300SD, 102K, wife's ride
1969 HD FLH, 45K, restored/hobby
1996 Chev Suburban, family taxi/tow vehicle
1990 John Deere Model 240
1942 John Deere Model LA
1985 16' 4Winns ski boat