fluid
Andy, Good points of observation as usual.
Fish, avoid additives as you can not be sure of what all is used in them. Some additives actually use brake fluid that swells seals and can actually cause rust as brake fluid attracts moisture from the air. Use a good quality fluid like Amsoil, Torco, Royal Purple as they are made with the necessary additives, but without seal swellers. I recently serviced a trans that had Amsoil in it for 40K + and the fluid looked and felt new. Synthetic fluids handle heat much better and don't break down and form acids and varnish like regular ATF. Synthetics also usually have a longer service life. If you are not in a position to do all the upgrades you might consider at least a shift kit that will raise line, increase lube and firm up lockup. E-mail me if I can help or answer any questions. I am located near Dallas. My. 02.
James Northum