Not a guru but I'll take a stab - sounds like T2 the yoke positon may have been shifted and its not centered anymore maybe? Ninja Gaiden could be either a simple H-size/V-size adjustment which you may have tried already or it sounds like your flyback is going out. What kind of chassis/tube is it?
I say if you have the ability to do the repair work yourself, you'll save a bundle of money, and its fun.. at least for me. Even if you replace the entire chassis its still considerably cheaper than shipping in a whole new tube.