Dave -

One more thought. Not to pile yet more work upon you, but consider replacing/rebuilding the vacuum elements while you have the dash apart. At the bare minimum replace the element for the center vents - it's inaccessable without removing the dash, and is usually the first to go. My hazy recollection is the other elements on a 123 can all be replaced without pulling the dash. (Someone please correct if I'm wrong.)

Modifying the system to use 100% recirculated air is quite simple, and does not require dashboard removal or any surgery. It's about 10 minutes work and requires about a dollar worth of parts. It is completely reversable should you not like the results. Here's a link to an article I wrote (in 1999!) on how to implement it. This is the archives of the original mercedes mailing list, which predates this bulletin board by about 7 years...

http://db.mercedes.cx/mb/199904/15/0010.html

The searchable archives of the mercedes mailing list are available via http://www.mercedesmailinglist.com

Good luck and enjoy,

- JimY

ps - I vote for the parallel condenser too. Why spend extra for the MB unit?