Refer to my previous remark. What is your rationale for believing that the pump would operate in the absence of a person on the seat?
It is important to note that a small number of E500 cars were sold in 2007, and among them, only few were equipped with ventilated seats.
The esoteric technology is used in other models, including the S, CL, and GL class. However, the majority of do-it-yourselfers and even highly skilled MB Master technicians will not have encountered the need to do maintenance on it. (C55, sometimes known as PCS, is excluded, etc.)
I have had a total of ten luxury vehicles, including five E500 models and five V8 roadsters, coupes, and saloons. However, only one of these vehicles was equipped with vented and multi-contoured seats, which I never found necessary to use.
A little online search reveals that the cost of the pump is a predictable £800. However, I am curious as to why you believe it is necessary to get a new pump given the existing one functions well when directly connected to a 12v power source.