I liked the improved rollers @humebeam posted, but I was having some real issues with them functioning properly:

1. They tended to rub against certain slots in the hydra which reduced their rolling smoothness (e.g. second from back slot often caused friction-creating collision with even the smallest roller).
2. The adjustable casings did not work reliably because the little lips would rub against the roller body.
3. The rollers themselves had inner holes that were relatively tight, such that screws used as axles could rub against them, again increasing rolling resistance.

To solve these 3 problems, I remodeled the rollers in CAD and implemented two fixes here:

• I shortened the overall top-flat length of the rollers by 0.5 mm on each side, which improves clearances between the roller and the hydra casing. It also fixes the clearance problems with the adjustable casing end-caps.
• I enlarged the inner holes for the screws to sit within by 0.2 mm, which should allow the screws to avoid touching the roller body.

With these modifications I get a much smoother rolling experience, I hope this helps others struggling with these like me. The end-caps are the same from the parent, just included here for convenience.