I don't know if I was reading Peter wrong... but all my experience and many statements by others and pure logic would indicate that getting the varnish out of those small holes in the valve body of an automatic transmission would be a good thing.. then drain to get it out of the system.. just like we drain oil out to do the same thing..
It is also cheap ( typically under $10 ) and I have never heard anyone claim they thought any damage occured using it ...
Varnish is not supposed to be in those tiny cavities with those little balls that control the hydraulic clamping at the right speed and power of the clutch bands in an automatic trans...
I do not have any indication that this is a matter of new fluid being able to dissolve Deposited Varnish... thus I think something like Trans-X to get it off... and into the stream ...making it possible to completely remove it from the transmission via draining... is needed....
Steve, does that help ?