Thank you for your replies everyone!
Faster and Sailingfool, you've given me valuable information. I'm going to continue to look at CS36T's but I'm thinking this one is a pass.
Even if the mast brace leaking is common to all CS36's I have a bad feeling about this one - the engine was showing paint bubbling in places, I don't think it's been properly maintained, owner says he changes the oil and filters once in a while and doesn't know how many engine hours are on it - so I expect a full engine overhaul is needed. He also doesn't know how old the sails are, just that they're in fair condition, so I'd expect to have to replace them all. Doesn't know how long his anchor chain is?! Doesn't seem like the sort who keeps logs...or he's hiding something.
So while it's an extremely good deal, this one is probably a rescue.
Sailingfool, thanks for the warning, but I expect to pay more than $5k/year caring for any boat of mine. It's just that I want a boat I can purchase and then immediately liveaboard, so I'm looking for one in very good condition and which won't need any structural or major repairs.