Me 2003 7.3 4R110 needs a tranny fluid change. It has 130,000 miles and I have only put 10,000 miles on it. I have no record of the tranny service being done. I have been thinking about going synthetic, but understand that it is hard to drain the T/C. Can they synthetic be mixed with what will be left in the T/C without problems? Any help will be appreciated. Thanks to all who respond. You guys are always a big help. Jim