autohelm tridata speed-temp transducer

[yzlian]

hello there, my old boat, a crealock 37, uses autohelm tridata st50, which has been discontinued by raymarine some years ago. now the speed-temp transducer has gone bad (the head unit has been checked by a raymarine technician and found to be ok). they are no longer making the original parts, so they refer me to a substitute. i did some research and found the following:

the original speed-temp transducer has original part number Z092, which was later changed to M78712, which was in turn changed into E26031. In the process, the inner diameter of the skin fitting has also changed, from about 41 mm to 35 mm, while the outer diameter has not changed. the transducer truck, of course has changed to 35 mm diameter as well. the wiring is a bit different but the head unit can still run this new replacement transducer, according to the raymarine people.

queries: is the above account correct?

if so, a replacement is the following:

Raymarine E26031 Retractable Lexan Speed/Temp Sensor

now when i look at the pic on the above webpage, i do not know what the little part that sits next to the main unit is. can anyone enlighten me on that?

also, using this substitute for Z092 requires a haul-out (but does not require re-boring). would be ideal if i can get a Z092 but i have searched the internet exhaustively without success. does anyone have a surplus that i can buy?

thanks!