Skoda Octavia impossible to select 1st gear

Check if going into gear o.k with engine off , if so USUALLY rules out gear linkage / selector linkage but not always . If ok , may be clutch / diaphragm fault

Tried resetting the two gearbox cables. Bear with. I set gear lever in home position using 5mm drill bit. I had previuosly released the two cables tri-fingers inside the engine bay. I tried to set home position for the crank shaped selector lever situated next to the gearbox but it wouldn't depress with the gear lever in the home postion! If I released the gear lever the selector lever would depress but the wee lever you must turn throught 90 degrees or turn to 12noon to lock said select lever in home position, would not turn no matter where on the up down travel of the selector lever I tried. I can confirm the follow checks have been carried out:
A) With the engine OFF all gears select smoothly including reverse - I thick this means the gearbox is OK.
B) With the engine OFF and second gear selected I can start the engine and pull away smoothly - thus eliminating a clutch problem
C) I have had the car from new and it's covered 148K and for a great many years (maybe 10) it has not had a gearbox oil change - probably NOT good!
D) Some time before this now "You must pay attention to me moment" I noticed a reluctance not to go into first and a tendancy to crunch for reverse, I overcame this trait by selecting second gear before reverse which worked.
That's a fair reflection at this point in time.
Thanks Whittingehame. Any other thoughts are all welcome.

Could check fluid level in clutch master cylinder and for any leaks , but every chance it may be general wear and tear on clutch assembly and time for replacing