Thanks all for your input and the sensor has been replaced.

It was an interesting day.

I called the local (canadian parts store) 'Lordco' store and was quoted for the sensor about $ 190.00(cdn) The local MB dealer wanted approx. $170.00(cdn) So for any of us that thought (myself included) that the dealer price was more expensive than a jobber - better think again.
So then, off I go to my local Canadian Tire Store and purchase a sensor for a 1990 Mustang 302 for about $50.00 Cdn. install it (had to change the connector by using the old MB one and soldering it - no big deal) and away I go and all is well.
I'll sware it runs better too.
Mind you this may be the same phenomina you experience like - "a washed car seems to run better".

Hope Mr Daimler doesn't turn over in his grave at the thought of a Mustang sensor in a 560SL but - oh well - he had more money than me and could probably afford it.

Barrie