MB gas sending units seem to be a weak area. The sending units were replaced twice under warranty (with less than 32,000 miles) on our 1998 C230 - once in the first 9k miles, and again at about 22k. And I would guess that the sending unit topic has probably come up here at least as often as the wiring harness and evaporator core discussions. I have taken to just filling the tank anytime the trip meter show close to 300 miles on either of my MBs, regardless of what the gauge indicates.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E