Thanks Dave and Mark,
I have never heard of this one before but did experience what you mean.

The plug on the ecu had oil in the bottom half,along with the oil switch plug and also a bit was back in the 02 sensor plug.
I removed the ecu and found it to be full of gel so the oil cannot get in.

Replaced the oil pressure switch and 02 sensor and told customer of the problem and asked them to return friday so we can check the 02 sensor plug again.(i think i will remove the seal in the plug as you suggested Dave)

thanks again Brad