The brief
The Golf had crossed 120,000 km, which on this engine is the recommended timing belt interval. The owner is a regular at the workshop and brought it in proactively, before any ticking or hard-start symptom showed up. A timing belt failure on this engine takes valves with it, so the conservative approach pays for itself the first time.
The timing belt keeps the top of the engine spinning in step with the bottom, and on this engine it also drives the water pump. It's a service item with a set life, and the belt, the tensioner, the idler pulleys and the pump all age together as one set. Wait for one of them to actually fail and you risk a bent-valve engine, so the job is preventive, done by the clock.
The diagnosis
With the covers off, the old belt was glazed along its ribbed face but still in one piece, the tensioner had a small wobble on its bearing, the idlers were fine, and the water pump, which this belt drives, was just starting to weep at its shaft seal.
Doing the belt and leaving the pump would mean a second strip-down whenever the pump let go properly, and you'd pay the labour to get back in there twice. So it was the standard kit job, belt, tensioner, idlers and pump, all together.
The work
The timing was locked with the proper VAG tools so nothing could move, and the old belt and tensioner came off. A new VAG-spec timing kit went in, belt, tensioner, idler pulleys and water pump, the timing set back to spec on the tools, and the cooling system refilled with the correct coolant.
Then the engine was run through a full warm-up cycle to confirm the belt drive was silent and the pump was dry.
A road test confirmed it ran clean through the rev range.
The outcome
Clean timing reset, a dry water pump, a silent belt drive across the rev range, and the most expensive single failure point on this engine taken off the table.
The Golf went home good for the next belt interval. A timing belt gives you no warning when it snaps, so spending the money on the full kit on time is the cheap insurance against a far bigger repair later.