1.4 TSI 170 HP Oil in the candle borehole? 1500 Euro Repair!

Hello together, On the Golf 5 GT my father-in-law soups. Workshop oil in the candle hole or in the well where the candle is. The oil runs down on the hot engine, stinks and burns, especially when the engine is heavy. Can you make a rhyme on the Master’s information that the repair should cost about 1500 euros? How does oil come into the well in the head where the candles are stuck? Did anyone ever have this at the TSI? Greeting, Jochen