I also second the "DO NOT FLUSH"
I recommend that you drain/remove the pan, clean the pan REAL WELL/Hospital clean
Also recommend DRAINING THE CONVERTER, IF IT HAS A DRAIN
Replace the filter, (most late model Fords have a re-useable pan gasket with metal in it, and IF yours still has it you can re-use it rather than using the one that comes with the kit.
I don't think I would introduce STNTHETIC fluid into a relatively high mile trans, just regular stuff, there should be a spec in your manual.....I'm thinking regular Mercon that's Ford approved will be just fine.
JUST DON"T FLUSH UNLESS YOU WANT TO HAVE IT REBUILT SOON!!!!!