BMW 2007 X5 3.0si, N70, E52K engine. My mechanic needs to do a gasket replacement and wants to change out the oil pan. His official prices for parts seem high. Any suggestions on websites where I can source OEM parts at a lower price? Any harm in using second hand parts? For instance, the official cost for new moonroof actuator/motor was $800. I found an OEM eBay used replacement for $35. Works fine.

Hi. 
I would have no issues using second hand parts as long as they are straight and clean. 
where are you based? 
Check realoem and put your vin number in to get part numbers for the pan, then eBay or the likes.. 

in the Uk, I use quarry motors for most of my bits. I’m sure they would post worldwide if needed. 
 

good luck