I have a Ford Focus 2012 (Hatchback) and after 9 years of prolonged heat, the windshield wiper tank cap decided to disintegrate. I whipped this up it Fusion 360 and printed it in PETG.
This cap may fit newer ford(s) vehicles.
Update:
I updated the model to be a little easier for some people, this is a push-fit with a screw-on lid.
Thingiverse: