Finland? Once you are done with 5W40 and 0W40, switch to 0W40 or even better 0W30.
Castrol 0W30 that meets VW 502.00 among other specifications in my opinion proved best in that engine.
Yep, Finland. If there is no severe oil usage I might be tempted to try Total Quartz 9000 Energy in 0W30. I ran that in my Lexus and it seemed to do a good job. Might try Castrol, too, but Total is a lot
I just don't know how hard these 1.8T engines are on oil.
Very hard! Especially 225hp version since hp was increased with more turbo pressure.
That turbo is cooking oil like crazy, and in the U.S. there was even law suit because of that on 150, 170, 180 and 225hp versions.
My friend used Mobil1 5W30 ACEA A1 (not VW 502.00) in Audi A4 1.8T with 180hp, and engine had a sludge bomb at 80K miles.
Europe generally have more selection of high end oils, so probably that TT was filled with VW 502.00. So make sure you use VW 502.00 oil strictly and look for oil that meets besides VW 502.00, MB 229.5, BMW LL-01, Porsche A40. New Shell with pure plus technology proved really good.