For what it is worth, the cadence unit doubles as a speed senor. It uses two magnets, one on the rear wheel spoke, one on the crank. I do not know if the GPS has to be disabled to use it for speed monitoring.

Yeah, my HRM usually bugged out in the same part of my ride. But only early in the ride before I got a good sweat going. Water just did not seem to do the trick. This is probably why the gel helped me out so much.

Good luck with the search.

-J