Okay, I just completed this job successfully and want to add some comments and corrections to this thread while they're still fresh in mind...
First off, C32AMG's guidance was extremely helpful and is accurate for the most part. A few exceptions:
1) The 2 fasteners that need to be removed are 5mm hex heads -- not 4mm. One of mine was very tight and I thought I was in trouble when my hex socket stripped the head of the bolt. Luckily, I was able to get a standard 3/8" to grip the top of the thing (with a few good raps of a ball pein hammer). There ain't much room to maneuver in there...
2) The bolts don't actually secure the modulator directly; rather, they attach a metal strip to the transmission body. This strip, in turn, clamps the modulator in place. Note that there's a groove that runs halfway around the perimeter of the modulator. Since the metal strip must be seated in this groove, you can use this feature to establish the correct orientation for the modulator. In short, the groove has to go on top.
3) Once you pry out the old modulator (I used a screwdriver), there IS indeed some steady oozing of tranny fluid, contrary to comments made above. Given that the fluid flows outward though, I suspect there's little risk of any contaminents being drawn into the transmission... The flow is extremely slow--akin to bleeding brake fluid--so if you're ready with the replacement part, it's a non-issue. But you should be aware that this would not be the best time to leave for lunch!
4) The vacuum connector winds up on the upper left with the modified replacement modulator for my 420SEL. The original part found its connector on the upper right.
5) Though you need to pry the old modulator out with a hand tool, it doesn't take much force to get the new modulator in place. (I kept shoving the thing expecting it to slide in further, but it's not necessary: the aforementioned metal retaining strip clamps it into correct position when you retighten the bolts.)
My old modulator was leaking under the cap, and the device was ineffectual in adjusting my steadily worsening shifts. I noticed an immediate improvement as soon as I took the car out for its test drive. The shifts are MUCH smoother and consistant now--and I haven't even made any of the pressure adjustments C32AMG expertly described yet. (I will probably just manually adjust the new modulator to
feel for now. It's getting way too cold here in New York to work outside, so I may not hook the new modulator up to a pressure gauge for "proper" adjustment until the spring... if ever.)
(Also did front rotors, pads, and repacked the bearings as long as the car was off the ground. Bottom Line: She feels like new---How I LOVE this car!!!)
Hope this follow-up proves helpful to others. Thanks again for everyone's support here.
Cheers!