My answers are as follows:
1. A compression test showed low pressure on cylinder 2
2. Sometimes the very light blue smoke is dense smelling mostly of petrol; at other times it is slight, but still smelling of petrol. The smell of petrol pervades both the engien compartment and the interior of the car.
3. A sort of 'rattle' noise is now there continuously but was not in evidence leading up to the first morning when it suddenly happened (when parked up the night before it had been running perectly!)
What I omitted to say before was that after the injectors were 'flushed thru' during a major service, the engine worked perfectly for about 5 days when, whilst idling, it suddenly went 'lumpy' and the smell of petrol returned. It has remained like that. My tame garage suggested it may be a sticking valve but they were not familiar with the W124 Mercedes engine.
3. Yes, the engine is misfiring - 'lumpy'
4. There does not appear to be oil in the exhaust. As I say, the overwhelming smell in the exhaust is of neat petrol.
6. This is an interesting question. Prior to the incident, I noticed that the temperature gauge on the instrument panel was barely registering so I assumed the 'thermometer' unit in the top of the block had failed and asked for a new one to be fitted. It was, but there is still barely a reading.
Does this help?