It could also be that the slave cylinder is faulty or needs bleeding (it's a hydraulic clutch on a tdi). If the clutch doesn't fully disengage when changung gear, shifts can require more stick effort, which like @weslangdon says can cause the syncros to wear. Usually the little teeth on the brass ring become rounded off- easy fix/swap, but gearbox needs to be opened up to do it. Same gearbox as the tdi 9N polo if that helps...