I've got a fouled up fuel sending unit on my C230K. My local friendly (but REALLY expensive) MB dealer told me this part is located just under the rear seat and can be changed quite easily- for 400-500 USD. When I go online to find the part, I find there are two sending units shown for the car. Does anyone know which sending unit I might need and if the job is fairly straightforward for someone with average skills (me)? Also, a recommendation where to purchase this part would be appreciated.

Thanks so much for your help!!