It's a bit of a pain on the w124! You have to remove the boot between the turbo and MAF, and I also had to remove the sensor immediately in front of the housing (22mm offset box wrench). You have to make sure that you align the little tab inside the housing with the recess in the thermostat, or everything will appear to bolt up fine, but it will leak. I made the mistake of assuming that the check valve needed to be at 12 o'clock. It definety isn't. Please don't install it 4 times, thinking you may have a cracked housing or worse. Look for the little tab!
Hahn Rossman
www.alkifoundry.com
1981 TD
1987 TD