Here is a thought that I have regarding "some" of the intermittent dash warning light problems......
My 300D has an intermittent Seat Belt warning light....sometimes it comes on for a bit, kinda annoying at night......and it used to have a similar problem with the Front interior light...but it fixed itself over time....
I have mentioned before that I have a bunch of experience on large German Diesels from my seagoing daze

...well the ships have a lot of electrical / elektronik stuff.....one of the problems that we had was our used 20 yo ship used to have various relays and timers drop out for no reason.....drove my electrician and a couple of engineers nutz......but we discovered that over time, wear, use.....some German components tend to weaken in the magnetic solenoid area....allowing the timer (or whatever) to drop out....causing the contacts that it controls to open or close......
I have not looked for a schematic of the Glow System this AM...but from reading here, I understand that the indicator light is on a timer that is unrelated to the Glow Sequence......perhaps the timer is getting weak and dropping out, just lighting the warning light.....pay attention when you hit sharp bumps/potholes and such.....if they seem to go together, don't worry about it, too awful much !!!!
Folks, bear in mind that this is a Theory...with no proof, but I quit worrying about my seat belt light some months ago.....
SB
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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG