Well, I rebuilt every part but the gearbox, thinking the bike has so little use on it that the box would surely be ok? So I get the whole bike back together, every bolt & nut lock-tighted, about ready to start it for my first time but first put it into each gear and rock the bike back & forwards as a general check, well bugger-me, in top gear the engaging-dogs slip! So tear it all down again, find it needs three gears on the mainshaft and the centre shift fork :-(
So there you go, unless you are buying a bike from a true enthusiast, check every bloody thing! I shoulda realized, all three KX250A5's that I bought had to be rebuilt from the gearbox & crank up.