I like most assumed the dealer would be the worst place purchase parts from, but time and time again they can be a surprisingly cost effective source. Yes you have to do your research but there have been many times in the past for my old XJ and now for the XF I am finding they are not only better priced, faster delivery and hopefully the correct part.
The latest example is the supercharger drive belt, SNG (Who I think are great and have a superb list of parts) shows not only a different part number but also more expensive.

So for a 2017 XF 35t AWD the dealer has part C2D61183 at $67.76
If anyone else breaks the symposium vacuum line, it is part AJ812350. This was more from the dealer, but they had one to me in a couple of days and with delivery from 3rd parties adding to the cost, overall it wasnt that different at $25.99

So while every part is different, don't rule the dealer out when looking for parts.