Check the archives - I recall someone used a sealing product that was expensive but work well for them.

I did note there web address just incase I needed it - you might give it a try and report back before ripping the dash apart. Fortunately, I have no experiance with them or the product, so I can't give you recommendation. Perhaps others have used the sealer and can tell you good or bad.

Here is address: http://cryochem.com/dist.html