<VV> 66 PG Trans Cable Fix-Shrink Tubing?

[Johnbmcg at aol.com]

I have leaky transmission shift cable in 66 Monza 110/PG. Local Corsa  
chapter member suggested there is fix using shrink tubing with internal sealant  in 
lieu of replacing cable. Can anyone verify this works, and if so what size  
shrink tubing and possible sources?  
 
We're also trying to diagnose pesky downshift from high to low at freeway  
speeds (lots of noise and rapid slowing down..). Have replaced modulator, fluid  
including removing small gunky bits attributed to internal clutch, and 
rechecked  linkages. Latest theory is low vacuum (~10") but have replaced hoses and 
found  no other major leaks.. Any additional suggestions?
 
John McGowan