My low fuel level light only comes on when the tank goes completely empty. Furthermore, once I get down to about 8 gallons in the tank, the fuel level gauge goes down to R and stays there forever. From what I found out from searches and from my own suspicion, this means my fuel level sending unit is messed up right? Just wanted to get the opinions of techs or people who have gone through this before I purchase a new sending unit and start the replacement task. Thanks. Oh, car is the '84 300SD.

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver