<VV> shifter help

[Devin]

Hey all- I'm a recent add to the list and am amazed at the knowledge out there.  My wife's daily driver is a 63 Monza 900, 102HP 4 speed.  I steal it as often as I can.  We bought it about a year and a half ago with 68K original miles on it.  Now for my question.

Occasionally as I am driving it, trying to hsift gears, when the shifter is put into the proper place for the appropriate gear, it is simply not there, still in neutral.  It feels like the shift gate moves somehow.  When it does this, I can put it in neutral and push the shifter back to the correct position by pushing between 1st and 3rd.  It nearly always happens going into second gear, although lately it has happened going into both 3rd and 4th.  I'm an ASE certified technician and have much experience in 60's era vehicles, but am not familiar with the workings of the rear-engine Corvairs. 

Any thoughts on what might be loose?

Devin