Today I drained transfer box.oil was very clean and no swarf on the drainplug.i removed the round cover plate and side plate,cogs and bearings look ok.i went into car and pushed hi/lo selector bar on box into high went back under used a large screwdriver in cogs leavered lightly between bottom of box and cog and got movement on both props.so would this suggest transfer box ok and clutch or gearbox next.

i was told by ashcrofts that inside the selector housing, the bar that connects to the selector cable has a 'boot' fitted on the inside which is held on the shaft with an allen bolt which can work loose, if it does you cant change from hi to low
its shown on photo 20
Ashcroft Transmissions

Thank you much appreciated. will have a look tomorrow