So it looks like i have finally cracked it

and have just returned from a test ride where I was able to gear up,down and even find neutral gear at junctions,Very Very happy (sunny)
Came down to a collection of things really but thanks must first go to everyone who posts and supports with information and their experiences on this forum,it really does help,Carlos your link to SteveioLaverda a great help (goodjob).
So here's what i did,........
removed the slack from the gear change spindle selector fork by bending one of the tangs slightly on the doglegged spring, that enabled any movement of the gear shaft to be directly imputed to the linkage and then passed on to the hooked selector arm.
Checked that the eccentric adjuster cam was forward facing,and with the bike in 4th gear adjusted the hooks to give equal movement up and down to the 2 drum selector pins.
Even after doing this and now with a more positive upward selection 1-5 it was still sticking dropping down from 4th - 3rd,I then loosened off the inner gearbox casing and let it find its happy place,also giving it a gentle nudge forwards.
All nipped up and checked with all gears selecting up and down a few times to confirm all was working.
Test ride confirmed a major improvement and a gentlemans box
Big thanks to all,now to get in that Jota groove (Lavflag)
Steve