Since you say this happening when you turn the valves after adjusting them, I would think the valves have worn in the one position and when you rotated them the valve face to seat contact point is changing. You may need to adjust the valves slightly loose doing the go, no go method (adj. the valve with the correct size feeler gauge slightly loose, and then check with the next thicker feeler gauge so it will go in with some force - but not too much force). Then, take the car for a spin (say 10-20 miles) and re-adjust the valves after the engine has cooled off for the cold adj. clearance.

The valves on my non-turbo 300D have a device called valve rotators and I believe the turbo 300D's have them also. The valve rotators do just that, they rotate the valves so they wear evenly and maintain a good seal. Since your valves had no clearance, there is a chance the valve rotators were not able to do their job and this is causing the change in valve clearance when you rotate the valves after adjusting them.

I don't know how you are adjusting the valves, but when the adj. nuts are tightened the clearance will change so you have to compensate for this. You will have to get a feel for this, sometimes tightening the bottom nut up will tighten (or reduce) the clearnace, tightening the cap or top nut down will loosen (or increase) the clearance, and tightening both about the same will keep about the same clearance.

You may need to adjust the valves again in a few hundred miles (or sooner if they start making noise) because they may wear in a bit changing the clearances.

Also, look to see if there are grooves worn in the rocker arms. If there are grooves, then you need to make sure you are measuring the area where the cam shaft contacts the rocker arm and not the the non-grooved area. I've looked at several non-turbo 300D's and have noticed that the rocker arms for cylinder's 1 & 2 will get grooves, but cylinders 3, 4, & 5 will not have grooves. I have looked at turbo 300D's and the valve train assembly looks similar to the non-turbo - so the turbo rocker arms may get the same grooves, but I have not done a thorough examination so I am extrapolating. I saw the same grooves on some Honda motorcycles (overhead cam and rocker arms) and all of a particular model would get grooves in the rocker arms - even if the valves where adjusted before the engine was ever started and then adjusted per the interval required and, in some cases, more frequently. The Japanese engineers could not or would not answer why this happened. Has anyone else seen this and, if so, did you ask the dealer, the M-B Rep, or say a M-B engineer why this happens?

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.