tranny on limp mode

My 97 e 420 was droven into a flooded street and inhaled some water into enginein .I drained all fluids, flushed engine and transmission and got vehicle running . The vehicle is in "limp mode" which means 2nd gear and Reverse are available only.
Brought vehicle to local Mercedes dealer to have codes scanned--came up with speed sensor issue inside transmission.
Is any body have had same problem,do I need new tranny ?or it can be sensor ,there to start ? Any advise will be very helpful

u got two choices, get the box stripped to find out it needs a part, get part fitted and have approx 3months warranty on the work (if that) only for it to go wrong again, or put a new box in it and get a full 2 yr guarentee on the new part. sorted.

have them erase all faults and readapt shift points. ALL OF THEM! I know it takes a long time but that should work. Whats the MB component name if they told you or left you a printout.(something like y1b3 ) You might be able to replace the sensor itself or conductor plate (I think they had those on 97's anyways...I might be wrong