Welcome to the forum.
So whats showing on the mileage counter? You will probably need a new timing belt and tensioner fitting at some time if you don't have any record of it been changed. You don't say the exact model or engine code but its going to be around.
Golf/Golf Estate (98-06) 1,9D TDI PD 1998-03 Engine code: AJM
Timing belt and Timing belt tensioner - Renew Every 40000 miles or 48 months
AJM engine -MY 2000 every 40 000 miles/60 000 km. AJM engine MY 2001- and all other engines every 60 000 miles/90 000 km.
If you want to know the engine code the one half of the Options sticker should be in the service schedule if you have one. The other half of this sticker is on the boot floor next to the spare wheel well.
This one is BWA 147kw engine.
If you want to know what all the Options codes mean type them into
VW/Audi/Seat/Škoda Option Codes Decoder