What has caused this engine fault on my 2006 Golf GT?

I purchased a Golf GT 1.4TSI 170 new in July 2006. Last July an engine warning light appeared. It was diagnosed as a faulty timing chain, which was replaced. My mileage was 58,736. The local dealer carried out the work and Volkswagen kindly paid half of the cost. Now another engine fault has appeared which the dealer says is a lack of compression on number four cylinder. They are unable to diagnose the problem (and provide any estimate) without dismantling the engine, which involves six hours labour. Current mileage is 64,280. Could the problem be related to the work carried out last July and how best should I proceed as I had intended to trade my car in for a new Golf?
Sporadic problems are starting to occur on turbo/supercharged versions of the VAG 1.4TSI (not the turbo-only 1.4TSI 122). I'd say the timing chain problem will be due to the maintenance regime. Timing chain engines need fresh oil at least every 10,000 miles. Peugeot/Citroen and BMW/MINI timing chains are also failing, probably for the same reason. The other problem might be induction because the turbo/supercharged VAG 1.4TSI can seem to suffer partial bore washout leading to premature bore wear.
Answered by Honest John on

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