Are you sure that's what you meant to say? We're talking about the negative side of the boost gauge, and you're saying that your gauge used to go more negative than it does now?
If you're worried about the turbos: you're not going to have a seized turbo and not know it. You won't be boosting (stock z). And if the shaft has play, (I'm assuming you have checked it) on what axis is it loose? There should be a slight amount of in and out movement, but none (or very little) from side to side.
