Ford transit diesel, clanking noise from gearbox, drives perfect noise is there in 1st 2nd 3rd gear but not in 4th. changed oil but no difference?

Its an irish ford transit 350tdi manual and a hard working milk delivery van, connect was the only nearest listing in the catogories. Thanks for the help Its an irish ford transit 350tdi manual and a hard working milk delivery van, connect was the only nearest listing in the catogories. Thanks for the help

its irish then please accept my humble apologies ,a worthy job that milk deliveries ,well i hate to say it but but your gearbox will require a overhaul by the sound of it ,1/2 gear brake band is worn hence the jerky changes as for the noise in 4th then i would need a listen and a drive .In my time i worked on the electric milk floats for the london co-op ,And yes i have worked on auto transits as well as the ambulance service used them a lot .The only advice i can offer here is to look for a decent accident damaged car of the same age like a scorpio or whatever and change the gearbox from the car into the van as the local ford garage will know what gearboxes are interchangecable here ,offhand without the year i couldnt say ,but a older tranny from a zodiac or a granada will fit into a york 2.4 diesel and these dont need a fancy computer to work either , its irish then please accept my humble apologies ,a worthy job that milk deliveries ,well i hate to say it but but your gearbox will require a overhaul by the sound of it ,1/2 gear brake band is worn hence the jerky changes as for the noise in 4th then i would need a listen and a drive .In my time i worked on the electric milk floats for the london co-op ,And yes i have worked on auto transits as well as the ambulance service used them a lot .The only advice i can offer here is to look for a decent accident damaged car of the same age like a scorpio or whatever and change the gearbox from the car into the van as the local ford garage will know what gearboxes are interchangecable here ,offhand without the year i couldnt say ,but a older tranny from a zodiac or a granada will fit into a york 2.4 diesel and these dont need a fancy computer to work either ,