Originally Posted by JaccoW

I have been riding a lot on the Batavus these past few years and done so with pleasure. While I have a few things I want to upgrade in the future (TRP RRL SR lever, new bar tape, perhaps swap over most parts to the more complete backup frame I have) one of the more noticable parts that's a bit worn has been the rear derailleur.
The Sachs-Huret New Success touring derailleur doesn't feel as crisp anymore and seems to lack the pressure to shift into the smallest cogs (highest gear) most of the time. It isn't the adjustment screw, I have tried that already.

I've been thinking of swapping it out with the retro modern SunXCD rear derailleur which according to several sources is compatible with 9/10-speed STI levers.
Combined with a pair of sexy Shimano Dura-Ace SL-7700 (index) bar ends, Microshift BS-T09 (index/friction) or Microshift BS-T10 10-speed (index friction) + 10-speed cassette this should offer indexed shifting as well.

What are your thoughts on this? Would it be worth it to swap the rear-derailleur? Is there a way to replace the spring and give it a new lease on life? Let me know.