For Todays GM cars, Synthetic is fine. Which one you use may vary how long you can leave it in there for. Running a non synthetic in Todays GM cars would pretty much cause you the opposite of leaks and cause all kinds of bad things just short of powertrain warranty issues. The 1.4T in question works extremely well on synthetic oils vs the semi synthetic minimum requirement.Any time I have put synthetic in an older motor its caused leaks so do not want to go there.
This is not an old engine. You need synthetics in order to keep the turbo from eating itself in the long term, and with GM's gen2 dexos1 spec, all GM vehicles will be filled with synthetic if serviced at a dealer. The days of conventional oil are done. If your engine has leaks, replace the gaskets/seals causing those leaks. Deposits that old oils left behind to keep seals from leaking will also stick to modern low-tension piston rings, causing the vehicle to burn oil, and will also destroy turbos in short order.Any time I have put synthetic in an older motor its caused leaks so do not want to go there.