i had no luck getting any help anywhere with this so i decided to tackle it myself.
i looked at the wires going to my fuel tank and noticed a blue wire with a black line identical to the one on the wire harness that connects to the back of my cluster on the fuel gauge side... so i decided to take pics of what to do
Step one is to remove the cluster and pull it out so there is more room to work with the harness, you can also pull out the cluster half way and work around it if you have small hands. i went to the scrap yard today and clipped a harness off a c280 so i can take better detailed pictures, im sure they used the same color wire blue/black for a lot of other benz's but back on topic.
once you see the wire harness you want tocut the zip tie holding the wires at the top (circled in yellow)
then slide the tab at the rear of the harness down.....
Step two you can slide out the harness from its shell
step three you will notice the blue/black wire (red circle)
step four there will be other wires sharing the same slot with neighboring pins, gently pull out to expose the pins that are in that slot bar
final step 5 when the pins are somewhat exposed what i did was get a fine tip object i used a sturdy wire with a small tip and pushed down on the pin (circled in red) not too hard just enough so it will get better contact.
once i did all that i put back together in reverse order installed the cluster and the gauge has no issues at all! took a few days to figure this one out on my own but hope it fixes your problem! good luck!!