Well, here's the after action report: The problem seemed to be resolved by unplugging/cleaning/plugging the connector that the front sensor harness was plugged into. I did this while swapping sensors as per SSdoxie's earlier suggestion. So far...so good. Since this was an electrical problem that was kinda intermittant, we'll see if it comes back. Prior to the "fix", the 50-13 code would be thrown about 90% of the time when I fired the TC up. I have not encountered the problem since...but I've not put even an hour on the machine since the fix.
Possibly more relevant to the readership is the deterioration I found on both front and rear sensor wiring harnesses/pigtails. Specifically, at the sensor end of the pigtail, there's a flexible boot that shields the sensor body/wire interface. This boot was completely shredded on both sensors. I don't know the cause; however, the "rubber" the boot is made from was very thin and unimpressive. There's also a thin boot on the other end of the sensor pigtail that interfaces the pigtail to a 4-pin connector. This boot on both my sensors was perfectly intact...but it was also very thin material and it tended to slide off the 4-pin conn. and expose the wires to the elements.
I got some good quality electrical tape and thoroughly wrapped both ends of the pigtail. I then coated the tape with some of that "liquid electrical tape" (got it at NAPA) to seal the critter. Seemed to work great.
Also, on my "D", it was recommended that after 1000 hours, that the transaxles be drained and refilled. My service manual states that each transaxle takes something like 5.5 quarts. Actually, I found that the transaxles together took about that much. Just to be safe, I'll check the fluid level after I put a few hours on. FYI, the BC p/n for the speed sensor is 6684443 and the p/n for the lube is 6687120.
