2008 SR5 4WD. The tires are about 2 years old and have decent tread left. I got a flat and am not wanting to replace all 4 tires, especially since the other 3 have life left and I don't have $800 laying around. Additionally Cooper doesn't make the AT3 anymore. How bad for my car, diff, 4WD, etc, will it be to run a new tire with the other three used ones?