Originally Posted by A. Rosich

The evaporator issue on W140s is the SAME for all model years, the difference on 98-99 models is that they have not been around as long as previous models, so they haven't started to fail yet.

The culprit lies on the original design by M-B, which mixes alluminun and copper (two materials that don't mix well). The leaks on the evaps always occurs at any of the multiple junctions of those materials.

There is an aftermarket unit that address this problem successfully, which is build entirely with copper. I did put this unit on my E 320 T when the original evap failed. It is warrantied by the manufacturer for TEN YEARS! Any leaks and they will replace it free of charge (including labor).

On the other hand, the original M-B evap is just a betting game, it could last less than year, it could last up to five. It all depends on your luck. If it lasts more than five years, consider yourself very lucky. That is why I will always consider original evap fixes by M-B a tricky solution.

There is a full copper evap for the W140, it costs about 40% more than the original, but it is worth its price.