Good to hear things are working. It's a common problem, in some cases I have had to take off the hand wheel too, clean and lubricate both the inner of the wheel as well as the metal rod it slides on. The generous amount of oil seems to make a difference.
What was wrong with the original bobbin winder, it might just have needed abit of cleaning tuning and oiling, maybe a new bobbin tyre.
As you well know, a 99K should run light and smoothly when sorted out :- )