quite a bit mileage there! from what ive been told its best to do it every 70-80kish or every 4-5 years but thats only what ive been told. i wud make sure you get the belt changed from VERY reliable dealer if you dont go to the vw garage because it can cause some serious engine damage if it does go wrong. just think of it this way - pre-empt the task. i.e save for it now before it goes completely and save that bit extra and get it done at the vw garage thats what i would do.