I too have "worn out" a 1971 NR rear changer. It is now all rebuilt, cleaned
up and ready to go back on my 1976 Grandis Special Gran Prix that I just got
back from Cyclart.
The point is, these old changers tended to oval out the holes where the
pins go into the parallelogram body. The fix is to replace the pins with
oversized ones after slightly enlarging the holes to a round configuration
again. I think that Campagnolo used to offer a repair kit for these years
ago because both my front and rear changers have been rebuilt using this
technique. I personally like the old NR changer and it shifts as good as it
ever did.
Cheers!
Keith Kessel