The GF has a 20+ year old Univega mtb that is heavy and beat. But she has pedaled around Ireland, San Fransisco and NYC on it and is quite attached to it. The chain started jumping teeth lately until finally it broke. Everything is original so I figured I'd replace the cassette and chain. Not so fast! The Park lock ring tool I have doesn't fit, even though it looks like it should. I took a look at Sheldon Brown's site and it looks like I have a threaded on small sprocket, probably a Uniglide hub. I have not yet been able to budge it to get it off. Tried heat and penetrating oil and two pieces of chain with vice grips. Before I bring it to my LBS, what else can I do? I don't want to spend $$ on this old clunker. At first I figured I could score a $15 cassette at Nashbar and I'd be good. Now I see that isn't so easy with a 6 speed. What to do?