I figure at a minimum I need at least a freon charge.

The unit runs all the time, never seems to get cold enough, so at a minimum likely it needs a freon charge... but it is R-12 refrigerant, which is no longer allowed in the US. What I was wondering is has anyone done a change out of R-12 refrigerant, and what did it require. For the AC in my car, it means a change out of nearly every part. If it is the same for the boat, then perhaps a newer unit is a better solution.

If it worked fine, I would not mess with it.