4th gear crunch

hello people im new too this landy stuff so be nice..just bought my first disco manual on a p plate just came across a few problems .
{1}4th gear seems too crunch when changing from 3rd to 4th and from 5th to 4th also noticing the gear stick doesnt sit in centre, just sits over 1st and 2nd...
{2}also transfer stick will not go into diff lock.:doh:
going too try changing the oils very soon, to see if this helps
please can anyone help??thanks

gear stick bias plate probably broken to give misalignment ,4th gear baulk ring or worrse worn brgs allowing input and mainshaft to misalign hi/low diff lock shaft seized in housing

this dont sound too good where do i start

check oil if poor and full of metal fillings think about getting it fixed or replaced,diff lock lever usual needs penertraiting oil and effort or at worst stripping ,bias plate can be replaced or welded geares should fall when stick let go inline with3rd/4th

if i get the time at weekend i will have a play thanks