Is rear axle offset common with these cars?

Hi Folks,

After installing new 18" Saleen rep wheels with new tires on my '02 GT, I noticed the rear wheels were slightly different from left to right.
The axle appears to be offset to the passenger side by about 5/16".
I did do some Googling and found other people reporting the same...so I guess I'm just trying to confirm if this is common or not?
The car has not been damaged and has had no body work that I'm aware of. Mileage is fairly low at about 70k miles.

I stuck a 5/16" spacer on the left rear wheel, and they are now both perfectly even side to side (about 1/8" inside the fender).
Anybody out there running a spacer on one side only?

I don't know how thick of a spacer I can run on the stock studs, but I'll install longer studs if need be. That's not a big deal.

Just looking for comments or experience from the BTDT crowd. Thanks all.

Thanks for the replies folks. I'll check it over to make sure all is well under there, but being off a bit off from the factory wouldn't surprise me either.
I've had a bunch of 1980-1996 Ford trucks, and sometimes they were way off...completely different of course, body on frame, but still.