Black Phosphate Treatment?

Stuff that was originally black phosphate will be all rust now. K member bolts are a good example. You can wax them and it will hold up well. Just throw some more wax on them when you do an oil change.
I have a commercial guy I send my stuff too but caswell sells DIY kits and they work well.
https://caswellplating.com/black-oxide-kits.html