I have a bunch of older machines that the stitch length is off. None of them seem to be adjustable, but they do move from 0 stitches to the high stitches, even if the actual stitches doesn't agree with the numbers on the adjuster.
If the feed dogs move when the stitch length adjuster is moved, I'd say just keep oiling all the moving parts. Hopefully it will free up.
And one more thing, all of my long bobbin machines are noisy. Well, noisier than a round bobbin machine anyway.
Joe