I've just had my Ed30's 2nd service carried out at a local VW MD. The first service oil used was Helix 5W30 (previous owner and different VWMD) and now my local has done the second service using Helix 10W 40.
I asked them about this and they said the 10W40 is better quality oil....is this true?
Nope. The 10w40 is most likey a semi-synthetic - so how can that be better than a fully synthetic (from the same oil company). In a turbo engine - you categorically do NOT want semi-synth - you will coke up your turbo bearings.
This is just another example of main stealers being incompetent. ETKA categorically does NOT authorise anything other than LongLife 3 oil to be used in the GTI, even if it is on T&D servicing - so go back to the stealer and demand they change it for the correct oil.
Can 5W30 and 10W40 be mixed as i still have nearly 1L of 5W30 left as top-up oil?
Yes, they can both be mixed (though ideally no more than half a litre).