you say "the boat is new to you..."
perhaps there is a catch or other locking device that you haven't found yet...?
... previous owners modification maybe?
... perhaps something the boat yard put in to hold it up?
just thinking outside the box there ...
Beyond that, well your only option has to be a bigger hammer/lever - if the boat only weighs a ton then there can't be any real weight in the CB so bobing around in a seaway won't do ****.
reversing the jam effect of a ton weight is not so hard if you can get the leverage onto it.
... if you can access the housing that it slides into - clamping pressure for and aft will naturally open up the sides - not much but all you need is clearance