Just FYI, the water pump is normally replaced when timing belt is replaced; I think @ 90k miles on your car. Check the manual.

Don't put stop-leak in it. A bad seal is the likely culprit. It might be a little early for the belt, but it might make sense to do it now too, just to keep from having it all torn down again in 30k miles. I used to know the cost on that job, but it's been a while since I paid labor on anything. I would think that the bill should be somewhere between $400-500 at the dealer.