eek hekp - O2 sensor probs?

[tonyb]

My mk2 gti  8v (digifant, engine PB) has intermittent rough-running issues which, from various overseas chat groups, seem to be an O2 sensor problem.  I think this is a UK-market car, it was purchased new from the factory with the tourist-delivery scheme in place back then. I can see what looks like a sensor on the exhaust manifold, with a cable (looks like a stiff co-ax cable) running to it from a grommet in the firewall.  The cable is broken (at the sensor)and has an electric wire inside it.  I cannot find any sign of an O2 sensor for this vehicle with VW Heritage in the UK. Symptoms are sudden v rough running, sounds like its on 3 cylinders, smell v rich, wont rev much above idle, then it suddenly 'clears' and is fine. For a day or 2. Everything I read about Digifant systems is that this is a likely culprit for probs, on any engine with more than 100,000 miles.  I's like to replace it, but cant find one. Anyone got any ideas, similar issue, etc?