Extensive damage can be done to a 4WD timing belt by abrasive dust, which is an inevitable consequence of timing covers not being dust and waterproof. This is just one reason why 4WD vehicles that are used in extreme conditions need more regular maintenance than the log book suggests!
While timing belts are typically replaced at about every 120 000 to 150 000 km, this applies to vehicles that are not used in extremely dusty conditions, are used to cross deep-water obstacles, or are used in ways that place extreme demands on the vehicle as a whole.
For instance, almost all deep-water courses/obstacles contain abrasive dust; when this water enters the timing-belt cover, some of the abrasive solid particles that are suspended in the water stick to the timing belt to form a sort of grinding paste that wears away the belt, as well as sprocket teeth and the bearings in idler pulleys and tensioning devices.
The reality is that failing to inspect the timing belt and associated components regularly means that the timing belt could fail suddenly. This is not just a major inconvenience; on some engines, a timing belt failure could also destroy valves and pistons, which is really, really expensive to repair. Just one more reason that more regular servicing of your 4WD can save you time and money.
Your Repco Authorised Service centre is qualified to service your 4WD, no matter where you plan on driving it.