Have just replaced the vacuum modulator device (it was indeed broken!)with help from mechanic friend and a posting in this forum from dieseldan44 of 6/3/07 - thank you! I just need to know the correct pressure setting required for the 722.358 transmission unit and then my car will be back on the road.

I would suggest that unless you have proper ramps - or - jack stands that you have this work done professionally as you do need decent clear space under the transmission to work and a pressure gauge and fittings. It should not be too expensive (an hours work) most especially as you know the problem - the vacuum diaphram is broken allowing transmission fluid to get round it and to be sucked into cylinder 6 via the tube connected to the intake manifold. Makes sense once it's explained to you (as it was to me after months of looking for leaks!) - but a somewhat uniquely Mercedes way of managing things. By the way, the local Mercedes dealer was no help - only interested in selling me a new model!

Your comment about no effect felt by disconnecting one plug at a time is normal - one of the beauties of this straight 6 engine - I reckon I drove for thousands of miles with cylinder 6 not working due to the transmission oil pumping through it. By the way, since this fluid does not burn, I only occasonally noticed smoke - just had to keeep adding more fluid.

Good luck with all this.