c3 transmission question

I have a 76 smogger that I have had since new. It has about 120K Miles on the clock.
I have had the xmission oil changed twice, last one about8-10 years
ago and maybe 15K miles ago. At that time I had it flushed at the dealer - a fairly expensive proposition if I recall correctly.
My problem - When the beast is cold, it will not go anywhere for a little while until it warms up - the transmission does not seem to engage. Once it is warmed up it works fine - no slippage, fairly solid shifts, etc.
Now I must admit it does not get a lot of use now, so maybe that is part of the issue.
I am suspecting maybe something needs to be changed or checked, but I doubt it is a new tranny. I am thinking it is a case of something sticking or being a bit clogged. Or maybe something run through a part to be loosened.
Any ideas? I have to do a fair amount of work to it this year (new composite spring, shocks, brake seals, etc), so am just getting my ducks in order for the various things I need to check and repair.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.