When I bought my Tempest several years back I found the same thing. The seat had been carelessly drilled and was very crooked. I removed it and found that one side had been drilled incorrectly twice and that redrilling again would create overlapping holes. What the heck, I redrilled it anyway, remounted it straight and it hasn't slipped.
If your boat is new and your dealer nearby it wouldn't hurt to touch base with them, otherwise just try redrilling and see how that works.
Eventually, I pulled the WS seat out altigether and replaced it with a foam seat.