The early servo (71-74 thru ch. #2142110465 in the U.S.) was part #211-611-905. Not available OEM, there's an "aftermarket"
version available from http://www.wolfsburgwest.com" onclick="window.open(this.href);return false;, http://www.busdepot.com" onclick="window.open(this.href);return false;, and possibly others. I got one from WW and found it
unusable. I've heard one other report on that part, which was, in its entirety, "no problems".
The later 74-79 ATE servo (original VW part #211-612-103A ?) (ATE part #03.6850-0502.4) interferes with the L. parking brake
cable on my U.S.-spec '71 kombi by about 1/4". The smaller original (I presume) ATE booster currently installed has about 1/16" clearance from
the cable. One possible solution to this problem I envisaged was to cut loose, bend, and reweld the chassis tube the cable enters aft of
the booster. What I actually did was to acquire all the necessary parking brake components from a later model bus, to be installed when the
time comes to replace my current servo with my new ATE unit.
There's also an "aftermarket" version of the later servo from the same sources mentioned above.