Triumph Repair: rear axle comes out, rear axle shaft, trunion

Question
The rear axle shaft has come out of the U-joint assembly for the second time
now, shearing the retainer pin, on my 1980 1500 Spitfire. The first time, I
rebuilt the trunion and replaced the U-joints on both sides, and torqued the
spring bolts to spec. Since buying the vehicle last fall, I have only put about
600 miles on it. The rear spring, purchased from TRF, was replaced in 2002,
and the previous owner put about 6000 mostly carefree miles on it after the
replacement. What do I need to do to make sure the axle shaft doesn't come
loose again? Thanks for any suggestions!

Answer
I would suggest getting rid of the old axle assembly and replacing with a new or used.  More than likely the splines have worn where the yoke attaches.  If that is the case, then the play that is there will just get worse and worse.

Hope that helps.