It is not my impression that the syn ATF will do the job that Trans-X will... in fact in worse cases it is a two step deal... according to the instructions on the can.. you use it at a slightly higher concentration for the initial attempt to dissolve the varnish built up... then keep a lower percentage for regular use..
The reason is can work is that trans fluid deposits stuff which looks like varnish ... and the holes in a auto valve body are REALLY Tiny.. and some have check balls in them... like 1/8 inch in size... so if you get enough varnish to keep gravity from letting those balls cover the opening they are assigned to then you have a leak... the fluid will not be going to only the route it should be....and various problems can then occur... not the least of which is that the hyd clamping mechanism for the clutches will be less forceful than they should be and that is the same as riding the clutch in a manual car...
Flat wears out the clutch material...