I went through a similar situation with the st60 Tridata and Raymarine said it could not be replaced so I contacted Airmar and they had a replacement. I did finaly go with the new ultra sonic speed/ temp sensor. Raymarine also said it would not work but Airmar said it would and it is the best thing ever for speed. no moving parts and always dead on.
"FULL TILT" SOVEREL 33
"GOLD RUSH" PRINDLE 16