My first AR is a basic 20" A2 version.  It doesn't get much use anymore.  It funciton fine, except the front sight base seems to be rotated slighted.  This requires the rear sight to moved about 3/4 to the right to be zeroed.  This is annoying more than anything.  Is there an easy fix for this?  

Hmmm

Quoted: Whack it with a rubber hammer.

I would not do this myself.

D_H is an accomplished gun guy, and may feel comfortable with it, but I am not

I would encourage you sending it to Bushmaster (I assume its a bushy because they are well known for canted FSBs) or whatever maker you have.

This situation may include a binded gas tube, or other related issues. Best handled by the experienced or certified AR armorer.

i have done a few with a rubber mallet and its fairly simple.

Whacking it with a rubber hammer does indeed sound a bit crude.... but the amount of cant should be quite small if it is on paper. It might work but it is VERY inexact.
You could be whacking it from one side and then the other and so on and so on.
Who made it? You may should consider sending it back to the factory but I am sure they have tolerances of error that may or may not sit well with us.

Good luck
Bill

another one for "whack it" what do you have to lose ? if it works you saved a few months of being without your rifle, or if you have an AR-15 wrench, and barrel blocks, remove the gas tube loosen the barrel nut tap the front the direction you want it to go and retighten the barrel nut, if you have not torn down an AR-15 and rebuilt it, this may not be a job for you, but the more you "tinker" with an AR the more you will learn about them, in my opinion they are the easiest rifle on this planet for an amatuer to "tinker" with and learn about and build from scratch !!