i had this exact problem, i pulled the linkage rods of the gearbox, remove the clips and pull / prize them off, mine were siezed on but i managed to pry them off, also dont worrry they can only go back on one way so you can never fit it wrong.. one youve removed them get some wet and dry and clean the metal pins that ur rods just come off, grease and refit.
mine were seized solid and now its like new