300D automatic transmission shudders

I have recently noticed a mild shudder as my 1984 300D shifts from first to second. The car has 208,XXX well maintained, documented miles. I checked the dip-stick and found the fluid to be nice and red, and not the least bit stinky. It showed a bit low, so I topped it off with Dextron. The shudder can not be felt at every 1-2 shift. When it does occurr, it goes away quickly as vehicle speed increases. Can anyone give me some insight on what might be the cause of this? Is there aproblem with the transmission, or the torque converter, or the modulator, or...? Are there adjustments that can be made to reduce or eliminate the shudder? I am hesitant to ask for a transmission shop diagnosis. I am aware that the three-pointed star can be an invitation for a real screwing. As always, any advice is greatly appreciated.

It is possible that your modulator could be adjusted to firm up your shift a bit. This slippage is doing damage so get it taken care of. A good MB shop or a good independent AT shop should be able to check your pressures and adjust your modulator to spec to see if this corrects the problem. Ensuring that you have all of the vacuum lines connceted correctly and not leaking is a good start before a shop visit since vacuum controls the shifting quality on your car.