Just replaced the Butyl tape seal in back window of my 2003 reg cab ranger today. It was leaking/dripping down on top of drivers seat head rest.
Was an easy job and went well. Just pull back interior panels and head liner enough to get the 9mm nuts off (8 of them) then push window out. Clean off old butyl on window and cab with alcohol or paint thinner. Make sure you get these surfaces super clean with no oily residue left on them. New seal has to stick to both surfaces well. Got new Butyl tape seal at Car Quest - 5/16" (8mm) round x 15'. Cost $13.00 + tax. Put seal on window around outside of
the bolts and the join on the bottom. Put the window back in and loosely tighten nuts. Best to do this job on a warm sunny day with sun on back window so that seal will compress. You will have to push fairly hard all around perimeter of window to get window sitting back in to original position, but it does slowly go in. Tighten nuts up firmly but not overtighten. You could use a 1/4" seal but the 5/16" will seal up better. 3/8" will be too big.