Yes you are right though the cost of a gearbox oil change does bring tears to the eyes. I am old enough that £260 is more than twice what I paid for my first car! Though of course it is hard to compare an A35 and the E350!
I don't buy that they didn't know what car they were servicing, before it was in the workshop and given W212s have been around since 2009 a fair number of E350s must have been through their hands for a 3rd year service. Therefore to ring up just as I was leaving to go back to collect the car and double the cost of the service and implicitly suggest I was lucky they had the parts in stock so could do it there and then, was stretching my credulity. The oil change and the parts must have been a regular occurrence. If they really didn't have the appropriate service schedule for the car, then the whole system of electronic service records would appear to be not worth the paper it isn't written on!
As I expect the car will outlive me, it was bought as a last car, I suspect a full M-B service record is irrelevant and I will explore the local independents next year and make my own breakdown cover arrangements. Not for reasons of cost but hopefully a better overall service experience and so I don't have to make more mountains out of molehills next year!