Was installing new suspension on my 2018 f250 when I noticed the hose that comes off the top of the front, differential has a white cap and ends on the driver side engine bay has snapped in half. I cannot for the life of me find a replacement part for this. Any help would be greatly appreciated.

 

It sounds like the vent cap. Your best bet is a dealership or a salvage yard..

Certain parts are usually , "Dealer Items".
Depending on how long it has been missing and where you drive, might be a good idea to check the trans fluid condition. If it looks soupy or milky,, trans fluid and filter should be changed ASAP..