727 yoke seal leakage thoughts please

[oldcarnut]

My transmission yoke seal is dripping out the dust boot section.  Tranny is rebuilt and yoke is a snug fit into the tail shaft housing with no loose play.  I replaced the first seal because the trans sat in place a couple or more years without running even though it was a new seal.  The second seal dripped also.  It was a National brand seal and didn't fit as tight as the one that came with the rebuilt trans.  I pulled it out and installed a Timken seal.  It was a tighter fit on the yoke than the National brand but about the same as the original which seamed about right.  I also measured the yoke and put it in the lathe to polish out some light scratches with 500 and 1200 grit paper for a slick finish.  There were no worn grooves in the yoke shaft.  So I don't feel it's a seal issues after 3 new ones installed. Each leaked out the drain hole in the dust boot section or out the end if I rotated the hole to 9oclock position.  The yoke appears in good shape and I don't recall any leak problems way back before any rebuilding took place.  My next step will be a new yoke but if there are any suggestions I'd like to hear them before expense of a yoke.  It only leaks while driving, not in park running or off.

[alfaitalia]

My last yoke seal leak that took a while to figure (Mopar but not Charger) was caused by the faintest wear band on the yoke itself. It was so fine that I could barely see it....but I could just feel the roughness with a finger nail. I bought a new one as Id ran out of ideas.....never leaked again.....so look very closely at the yoke where the seal sits.

[John_Kunkel]

Be sure the leak is actually coming from the seal; there is a soft plug in the yoke that closes off the spline area and they sometimes leak and some of the soft plugs actually have a bleed hole in them that can leak fluid.

[oldcarnut]

I can see it dripping out the seal hole and there's nothing collecting on the yoke end.  I didn't feel any worn spots or deep scratch grooves.  When I measured it, it seemed pretty consistent down the length.  Is it possible the sleeve in the tailshaft is not located correctly from the rebuild?