After finally listening to that nagging feeling I went ahead and did the spline lube job on Big Red.
Everything went well. splines a little worn but ok. I used staburags on them and then reassembled the drive. Not a tough job, there is really
no excuse to put off doing it considering the consequences of neglect.
A short test ride and I noticed my rear brake pedal quite a bit harder than normal for just the first application, and greatly reduced rear braking . Then it returned to normal feel and stopping power.
Looking around and feeling things Quickly discovered a warmer than
normal rear brake disc. Not spit-sizzling hot ,just very warm, incongruous  with the light use of the brakes it had seen.

During the spline lub I checked the rear brake pads. They are getting thin, the end of their life, so they will be replaced this week.
The fluid was flushed & bled a couple of weeks ago.
Has removing and replacing the caliper during the service shown up
a brake problem? I was carefull not to pull or abuse the high-
 pressure hose etc. 
I guess some more spannering is on order before the pads arrive!
Anyone got a theory?

It's possible that the pads are sticking on the pins and binding slightly.

If you don't need to use the bike before the new pads arrive, I'd wait, then when fitting them clean the inside faces of the caliper and the pins thoroughly. Once that's done and the new pads fitted see if the problem reoccurs.

Hi there, I have found and you'll find it in other treats, that the brake pump piston return hole is small and tend to be clogged by the crude that grows inside the system. When this happens the caliper piston  would take longer to or even will not retreat, causing the heating.
It may be that the flushing perturbed the crude and clogged the hole.
Hope this helps.
Best regards
JAP

The new rear brake pads arrived and have been installed.
There was quite a bit of grunge built up around the pin and spring area,
so it all got cleaned up and everthing put back together.
Rear pedal feels good. So far no more binding or hard pedal, and disc feels fine after test run. We'll see how it feels after the pads break in.

So far so good Dale lets hope all will be OK.