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.
-Kyle '05 Dark Khaki (PJT) WK Limited 4.7L V8, '08 Overland Front End, Custom Exhaust, 245/70/17 GY Silent Armors, Bilstein 4600s, K40 Calibre DL Radar Detector/Laser Diffuser, CB.
Wife's Jeep: '06 Jeep Liberty KJ 4x4 2.8L CRD Diesel