You're going to 'go for' bubbles even though they look like a bad tiling mistake, distract from the smoothness, and make lines near the ends of the scrollbar that really are a mistake because you'd have to redo 16 variations to get rid of them? Wow.... the hardest working man in the theming biz grows weary! :-]

BTW you do know that those lines near the ends of the bars can be eliminated by carefully matching each one of the 16 little endcaps to a different position relative to the tiled fill. That's why there are all those little endcaps. Apple wanted those little bubbles so badly that they made the scrollbars the most complex part of the whole gui.... if not for them OSX probably never would have had that slow scrolling problem in the first place.