I bought a Super Adjustable razor for my dad for Father's Day several years ago. He used it a bit and didn't seem to have any trouble with it. But not too long after I got him the razor, he went back to using the Mach III and gave the SA back to me. I put it away for several years since I've been growing a beard, but found it in a box of old shaving supplies. The knob is stuck. I was able to twist it open, but it took more effort than usual. Is there any way to fix it without taking the razor apart? It's a cool razor and in really good condition on the outside.