Re: OK, WTF is the rear axle type?
If its bare metal primer it will work but will not be a durable.
The best thing to do is clean off the cover with rubbing alcohol really well because it has manufacturing oil all over it. Once its nice and clean and DRY, give it 2 to 3 Very LIGHT coats of Self Etching metal primmer. Do not worry about 100% full coverage, even 3 light misting coats will be fine. then paint multipul light coats of your final color.
2005 Dark Khaki (PJT) WK Limited 4.7L V8, '08 Overland Front End, Custom Exhaust, 245/70/17 GY Silent Armors, Bilstein 5100's and other mods.
My Wife's Jeep:2006 Jeep Liberty KJ 4x4 2.8L CRD