Ouch sensor repair cost
The o ring and electrical connector on the 722.6 transmission is a known issue.
leaks at the o ring wick trans fluid up to the tcu.
upgraded o ring and connector is about 8 bucks and you clean out the tcu and the wires with crc mass air cleaner.
diy is on several sites
www.benzworld.org w210 diy forum and others.
Takes just minutes if you do it in addition to the transmission fluid and filter change.
Someone is trying to rip you off if it is the problem.
A new transmission installed won't even run you $6500



