If its just the catch that is broken, I'd just push it in and try to secure in place with some adhesive tape. It's a fiddly connection and very brittle I found. If you need to replace it, you'll need to get one from a scrap dealer or the relevant loom from Ford.
Park uphill I agree, its a design flaw with water going everywhere when you open the tailgate. I'm fortunate I have a slope outside the house and try avoid parking it facing downhill whenever possible.