You do not need to replace both senders if one has gone bad. There is a wiring kit that needs to be spliced into the harness when installing a new sensor(s). The difference is the plug connection. You need to make that change even if you do both sensors.

I recently replaced the left side sensor on my 1995 C280. Make sure the tank is down. The lock ring can be rolled off by tapping with a hammer and a brass punch.