I have my wiper assemble out and decided to replace the AC Expansion valve. Do you just take the center nut off and it just pulls off? Also, what size orings need replaced and where do you get them?

The AC loses its charge in a few days and thought it would be prudent to replace the expansion valve while the wire assemble is out.

I just have owned the car for a few months and this is my first Mercedes.

Thanks,

Dave