Well last night so the return of the do-it-all tool, aka Hi-Lift Jack to split the prop!
Finally got the thing appart to reveal lots of muddy grease. Once all that was gone and everything was clean, despite looking in great condition things still wouldn't slide together.
The male side also looks in fairly good condition, all the nylon sleeve is intact.
A quick finger feel revealed surface rust / pitting on the female side of the splines. 10 minutes later after rubbing with the least abrasive things I could find (some green felty stuff frum under her kitchen sink!!) and things started to slide a bit better.
Lots of grease later and its almost like new - How long for though I dont know, I guess I'll have to check it in a month or so to see if the rust is coming back.
At least its saved me £75 for now!
Have Fun and thanks for the good tips.
Jon