Me too, I have this same modulator, the mechanics told me that there's no cap to remove, I just have to turn it clock- or counterclock wise to harden/soften the shift.
IS THAT RIGHT, nothing to remove and just turning it?

Well, I turned mine anti-clockwise and the shifts did become much better.

However, the range of movement is less than a full circle, so I don't know if you can take it off to adjust it further or not

1986 560 sl vacuum modulator
 

standing infront of the car where in mine (vacuum modulator )right or left all so
after i find it how or what do i have to do to tune it to the shifting my shifting from park to reverce is hard shifting but after the car warms up it seems to shift easyer .After in drive the car shifs fine .just if cold
Now the rpms are at 600 when i shift it

Help please new to this site
Richard