My '69 S22 has brownish drops of water coming out of the beam under the mast and inside the cabin. I am worried that there is rot and have read the post on beam replacement but first I am trying to devise a way of determining if there is degradation in the function of the beam without drilling exploratory holes. Here is my thought:

Unstep the mast, attach a rigid beam between the two chainplates about 2 feet above the mast mounting plate and attached to the beam to the chainplates with chain or cable. Put a car jack where the mast was, a bathroom scale on top of that and enough wood blocks to make up the rest of the distance to the beam. Force 300 pounds with the car jack between the cabin top and the installed beam and determine the amount of deflection in the cabin top over the mast beam.

What do you all think about this? Any idea on the amount of deflection I should measure?