Trouble Engaging Gears

Hi, my 2004 movano 2.5 cdti has difficulty going into 1 and second mainly, all other gears fine, does not do all the time but sometimes has most trouble when going from 1st to second, sometimes jumps out if i dont get it selected correctly, heard this is a seal or something in box, can this fix be done by yourself once gearbox is removed?

also how do you bleed the clutch on these vehicles?

Thanks guys