gearbox

[gringo]

transit mk5 smiley - mt75 gearbox
last night driving home my gearbox all of a sudden started making a loud racket like noise in 1st 2nd 3rd and 5th gears.
poor clutch but i nursed it 150 mile home in fourth gear.
could someone whos has the same issue pin point me to the cause of this.
i did check the oil level 6 weeks ago and gearbox oil was full.
anyone got a good working gearbox in lincolnshire, around the boston/spalding area ??
ta