That's the late 1970's S001, which was one step down from the Prestige's replacement, the SX100. The Delrin is quite flexible and, as system, the shifting effort was high. However, a lot of this was due to the levers. Switching to metal levers and a HyperGlide compatible freewheel makes a world of improvement. Still, some people had/have concerns of breakage. This can only get worse with age and environmental exposure, and a NOS derailleur will not be any more reliable. So, why not just go down to your LBS and offer $5.00 for a good, used Prestige, which most shops have lying around. Save yourself $20 plus shiping and taxes. Buy something else you need, like cables and brakes pads, and I wouldn't be surpised if they threw in a Prestige for free. I know, I would, if you had walked into my shop.