I have a regular rear axle, f150 2003 4x4 and just replaced the pinion seal as it was leaking, no noise or ill effect fron rear end. I was wondering if I should have used any modifier additive when I topped it up or does it have no effect on regular non LS differentials?

 

You don't need it.They say the additive can quiet noisy gears, but if you don't have a noise don't worry about it.