DESPERATELY NEED HELP! My '01 UK WRX is off the road AGAIN, for the 5TH time!!! You see, it's the Lambda sensor (apparently)....

Each incident has been brought about by the engine management warning light. The first time it happened I thought I had really shafted something, but after plenty of stress, wrangling, and a tow, I was told by the dealer that the Lambda (O2) sensor was buggered, and a simple replacement would sort it. Fine, sorted.....until it happened again.....and again........AND AGAIN! Each time they have changed the sensor in question, and it has lasted a limited amount of time. They did, at one point, suggest there were two sensors, both with the same part number, and they weren't sure which one they were installing!?! During the most recent occurence, No.5, they suggested that it was the seal around the exhaust manifold, so they had it off, fitted a thicker gasket and I think they also sealed it with compound. A few days later, IT HAPPENED AGAIN!!!

I'm at the end of my tether, but they (Town & County Subaru, Aberdeen) don't seem to know what it is. Can ANYONE shed any light on this problem??

Desperate, JD