Hi Mike,
I have a tempest 170 and went through the same thing. I used 3m 5200 to seal the point where the skeg cable goes through the skeg box. It's a common leak point on tempests. The box might be above the water line in perfectly smooth water but any bump or edging would let water in. If you're doing any rolling the rear hatch rim could be a point of entry for water as well. If you open the hatch and pour water around the rim you'll see it seeping in if the seal has been compromised.
There's a lot of good info on the tempest owners yahoo group. http://groups.yahoo.com/group/tempestOwners/ you're not a member you should sign up.....it's free and Steve Shearer, the designer of the tempest line is quick to answer questions and offer advice.