Luckily the burner valves are fairly easy to access, at least on the range these were on. Hardest part is accessing the 1/2" compression fitting on the back of each valve. Make sure not to over-tighten it when reassembling or you'll be in for a much more expensive and difficult repair!
New valves fixed the problems, they turn *much* smoother now.
Parts shipped very quickly, as advertised.