Didn't realize that there was a metallic structural beam down in there, but it seems that there is! You may have already found this thread:https://www.sailnet.com/forums/cal/58317-cal-29-beam-rot.html
which should be informative. They talk about inspecting under the settees for telltale rust, and how some beams have been replaced, and/or are stainless. Unless it has been fixed, a boat as old as this one has to be is likely to have some rust degradation. It can be replaced/repaired, but unless you do it yourself, the cost may not be worth it. If the beam is shot, it is both a value and safety concern. It is not going to get better, and the reason it is there is to support the structure of the boat around the mast. It impacts the structural integrity of the hull and therefore the shrouds that hold up the mast. So... give a good look to see what's going on in there.

 

I agree with Paulk. Not likely a boat this old that hasn't had the beam replaced is not going to have issues there. Only question is how bad it is.

 

It should be pretty obvious if the beam has or has not been replaced - my uncles 2-29 had a liner that covered the beam - it would have to be cut away to access the beam and it would be quite apparent if that had been done.