If (on your paddle) each paddle-and-contact assembly is screwed to its own metal plate, and has its own pair of pivots, you have an iambic BY-series paddle. [They're common; Bencher claims 140,000 have been sold.] The BY paddles have a spring which goes over a post, and the tension on the spring is _not_ adjustable. [The spring _force_ is adjustable -- see below]
If both paddle-and-contact assemblies are screwed to _one_ metal plate, you have a non-iambic ("single-lever") SP-series paddle. [They're not common, but they work OK.] The SP series has a spring that goes through a threaded rod, that goes through a post. The spring tension _is_ adjustable, with a nut on that threaded rod.
Look at the parts diagrams here:http://www.mtechnologies.com/misc/keyadj.htm#Bencher
It's likely that somebody really screwed up the adjustments. If your paddle is mis-adjusted, those steps should get it back into working order. PB-Blaster or some other penetrating oil might free up the screws. Avoid getting it on the contacts, and clean them well (with solvent) before re-assembly.
My suggestion if that doesn't work:
. . . Under the base, there's a screw that holds the "main bearing block" onto the base of the paddle. Take that screw out, and (unless things are really welded together) the main bearing block will loosen up and come off, and the paddle arms will be free to move.
If the paddle-arm contacts are really welded to the stationary contacts, you have a problem. Bencher sells parts, but the cost of parts (two paddle arms, two may be greater than the cost of a used Bencher.