Gear selector linkages

I noticed the other day that changing from 5th to 4th was becoming difficult and felt that the whole linkage felt quite firm. Its a manual gearbox, is it a cable or push rod selector and is it accessible to lubricate it.
Whats considered to be the best workshop Manual.
Thanks, Colin.

its not linkage or cable but a lever direct into box ,at the base of lever on the gear box top are 2 springs and a plate that hold the gear lever in 3rd 4th alignment ,if the plate breaks you get a floppy lever and no alignment so much harder finding 3rd and 4th , springs wear grooves into lever and can make lever stiff forwards and backwards ,pivot bush and a ball on the selector shaft ca stiffen , a fresh oil change with mt94 can help