Agreed. I put a new cap on the modulator on the Red Witch in July of 2016, and by late October it already had cracks.



A-HA!!!
I know exactly what you are talking about. Thanks!!!


The dark rings on the green plastic piston are the teflon seals in question.

 

Actually a huge improvement in the way the car shifts. Like driving another car. :-)

 

Yes, the adjustment did not fix it, the cap did.
When the cap is removed, there is not a vacuum signal to the modulator and the transmission shifts very poorly.

 

Yup, that's them.
Except they start life white. (Some have colored dots on them to help identify which one is which.)
Like any piston ring, they wear. This allows more fluid to flow past them.
Just installing "fresh" Teflon rings makes a rebuilt transmission shift much better.
"Rebuilding" a valve body is completely different than taking one apart, cleaning it, and re-assembling it....

 

NOTE to make the modulator rubber cap last a long time put some DC111 on it smear it all over,
the cap will last till your next transmission rebuild

 

Thank you! I have already started down the google 'rabbit hole' of trying to find Mercedes part numbers for these teflon rings. I will replace them at the 1000 mile fluid change after I get the Red Witch back on the road.