Thanks so much for the input, Joe.
About the issue on how to prolong the life of the evaporator, the service advisor at the local M.B. dealer suggested to always turn off the a/c compressor (switch to economy mode) about two to three minutes before my final destination, then raise the temperature on the temperture knob a few degrees, so some hot air will circulate on the system and dry off the evaporator on the process.
It is a tedious and annoying process, but after having to replace the evaporator on my E320T after ONLY 8,000 miles, I have become accostumed to do it all the time.
The evaporator used to replace the factory fitted one on my E320T was a full bronce unit, instead of the bronce/aluminum combination used by Mercedes-Benz. The supplier provided me with a written lifetime warranty, saying that if it ever leaks, they will replace the unit and assume the cost of labor to do it.
It is a shame they did not use the same unit for the S 500 when it was done.
CL 500, 1998
S 500 L, 1998
E 320 T, 1995