Rain, speedometer and the abs trifecta

[ahlem]

2001 X5 3.0 110,000 miles

On several occasions I've been driving on the freeway in the rain and the speedometer quits, the trifecta lights go on.
Both rear wheel speed sensors are less than 6 months old Bosch units.
I had the speedometer quit about a year ago in dry conditions with the trifecta lights coming on. I replaced the LR sensor first and solved the problem. The trifecta lights came on in the rain the first time last Fall.
I replaced both wheel sensors the second time around due to a low ohm reading that was probably caused by a questionable ohmmeter on the LR sensor.
Anyone experience this before?
I tried some boot grease at the seals where the sensor wires connect to the harness.