If any of you read my last post on Digitool readings and oxy sensors a few days ago you would have noticed that the conclusion was that the oxy sensor I had was shorting internally and Voltage from the heater was corrupting the signal to the ECU.  I was reading several volts at the Ecu (through the Digitool) on several occasions.  This was a intermittent problem which disabled the van- USUALLY associated with rain (and I live in Seattle).  I replaced the sensor yesterday with the "F**D" connector oxy sensor (U.S.  part # 13913).  Van runs great and all readings are normal.   
So I decided to look into the old one to see what I could find.  I ripped the "top" off the sensor where the wires exit and found WATER inside the metal cap and the rubber plug--- around the connectors for the three wires.  Also It looks like there may have been water in the main body of the sensor. 
So now I am wondering if there may be differences between oxy sensors?  Is it possible that some sensors are more suitable for exposed mounting like on the vanagon?  The old sensor I opened was also a 13913 F**D sensor with only 10-11K on it.  Anyway I intend to seal my new one well with oxy sensor safe rtv silicone.!
Nat 
Seattle