Mark,
        I have the same problem with the oil leaking from selector shaft seal.   I think this is just a good indicter that you have pressure building up in the transmission and fixing the seal will be a waste of time.   The time to fix it would be when you are getting the clutch done or some other big job when you have to pull the engine.   What happened to me is the end shaft axel seal popped off and oil leaked into the cv boot.   The selector shaft seal stopped leaking during this time.   Now that I fixed the axel seal the selector seal is leaking again.   My thought is that with age and wear the bearings are a bit loose and the differential produces more heat so that the oil pressure is higher than it used to be.   As long as you keep on top of the oil level you can keep driving but you may want to stick to 55 mph when you can.   You may want to check your axel boots for oil now and then.  Good luck, Gary

 ----------------------------------------------------------------------
 
 Date:    Tue, 26 Jul 2016 07:01:47 -0700
 From:    Mark McCulley <markmcculley@GMAIL.COM>
 Subject: Re: replacing transmission selector shaft seal
 
 Thanks Dennis. I'll check the fluid level and vent tube.
 There's no reason
 I can think of that the transmissions would overheat, still
 have the stock
 2.1L and don't pull a trailer. I did switch the type of oil
 I use a few
 years back, 3 years ago I switched from Redline to Delvac
 and then a year
 later I switched back to Redline when I installed a
 driveshaft decoupler.
 Both oils are synthetic 75W90. The transmission has just
 under 200K total
 miles, 80K since rebuild (I don't know if seal was replaced
 then or not).
 
 -Mark
 
 On Mon, Jul 25, 2016 at 7:08 PM, Dennis Haynes <d23haynes57@hotmail.com>
 wrote:
 
 > Yes this seal is easy to replace. However its leaking
 is usually a symptom
 > of something else going on. There is also an
 insert-bushing behind it that
 > may be cracked. Make sure the transmission is not
 overfilled and that the
 > vent tube is not kinked or otherwise clogged. This seal
 never sees enough
 > action that it should wear out. For it to go bad is a
 sign the transmission
 > has been over heating.
 >
 > Dennis
 >
 >