<VV> Advice needed on throttle shaft repair

[Charles McKinley]

Is there a methodical way to check whether my throttle shafts are worn  
to the point where I need to replace them? As far as I know they're  
still the originals on a '63 Monza 80 hp with about 80,000 miles on  
the clock. It appears from Clarks catalog that I have a couple choices:

1) try a set of their throttle shaft seal kits and keep my existing  
shafts (assuming they're not too worn);
2) buy new shafts;
3) maybe 1) + 2)? (i.e. new shafts plus seal kits - or is this  
overkill?)

The symptoms that lead me to suspect worn shafts are
1) difficult to set and maintain a steady idle at ~600 rpm.
2) sitting at a stop light, the idle speed tends to slowly decrease  
from, say, 1000 rpm to ~500 rpm.
3) Difficulty balancing carbs with Unisyn tool - the mixture and idle  
adjustments don't behave as they should. In particular, the mixture  
screws can be anywhere from 1.5 turns out to 5 or 6 turns out with no  
difference in the engine speed.
4) I've observed gas leaking from the throttle shafts onto the  
manifold, and it seems like this is a pretty good hint.

Advice will be most welcome!

Thanks in advance,

Chuck McKinley
'63 Monza 900 3-speed