Westend has it right - the white has aged off, the rubber base is showing through. I wouldn't reseal a thing just yet, I'd replace the whole darn thing.
The issue may be, as has been noted, how much damage has already been done. As mentioned, wood rot is a real issue, and the wood acts like a sponge. At first it just sucks up the moisture until it can't take anymore.
A few years ago I bought a water logged TT. I knew it was bad when I bought it, I don't think anyone has any idea how bad until they tear into it.
Camper Rehab