Can you find a good quality 5W40 fully synthetic diesel rated oil?
A 5W40 (or 0W40) synthetic will perform better than 10W40 for protecting your engine on cold starts. Faster oil pressure rise and better flow when the engine is not yet warmed up. 10W40 weight is old technology now so maybe it's best that you are looking at moving on anyway.
Here in the US our available brands are probably different than yours. But many of us here like the 5W40 diesel synthetic products marketed under Mobil 1 TDT/Delvac 1, Shell Rotella T6, Chevron Delo 400, and similar. Castrol's oils are also considered excellent quality though often more expensive, and you almost certainly have those.
European brands such as Lubro Moly/Liqui Moly, Fuchs/Titan, ELF, Pentosin, ROWE, and more are all very good also.
Many choices out there. Some people approach it like it's a religion, but in reality it's hard to go wrong as long as whatever you choose is a quality product. Look for one that meets the VW 502.00 or 505.00 or 505.01 or 507.00 standard which applies to the modern incarnations of this engine, then you will know for sure that you have something suitable.