Yes - you can buy just the adjustment bar. I'm sure they have it here on this websiet (I looked but couldn't find it). It's also available at Nacra dealers and at Murray's. I think it's about $30.

I had one on my 6.0 and had a terrible time getting even the locknut to stay tight...but I never had it stick before. I suspect someone put locktight or epoxy in the joint as you suspect.