Had similar problem doing emergency swap out with banjoed UJ on spline shaft. Although regularly greased, I still had to batter utter buggery out of the old one with Landy tool #1 - just to get it out. I had to do the same to the donor shaft.
Not great considering I was hammering next to the needle rollers for the UJ. :mil90:
Cleaned and better cleaned them, But neither the original or the donor would slide back in without melting wi the big hammer. Even trying different spline offerings.
At 9pm I took my biggest wire cup brush & a blowtorch to the bugger and removed the plastic coating - result ! finished at 10pm, drove to work next day smooth as silk. Really noticeable. Lots of reduced vibes/throbs/clunks. Mind you, it did now have a good UJ !
But, the question always was : "did I do a bad thing?" The way i look at it, I need the shaft n splines to move freely, including maintenance routines, more often than I'm bothered about accelerated wear! I reckon in the short term there is less strain on the UJ's and whole drive train, if the shaft moves freely. Maybe I will have a problem. If so another donor shaft is easy to source and lesson learned.
Now can somebody design a shaft, so I can actually get the fekn nuts off more than a 8th turn at a time ! Like gettin a socket on it or the head of a ring spanner. even better a ratchet spanner... grrrrrrr.