I really wish you well Crab, but I am concerned about your knees.
The fact that they are still bad, indicates that the problem is tendon, ligament, or cartilage. Any and all of which will get worse with the amount of running in boots involved in Basic training.
The thing about the army, is that if you have problems once 'in the fold', they will look after you brilliantly, but if you develop medical issues that prevent you finishing basic, you are out, and may not get a second chance.
If there is any way you can defer, and get your knees in better shape, I would suggest it as your safest option. I really would feel bad for you if things went wrong