Bojan, Im not as ignorant of conditions on the Eastern Front as you think. It got dusty, I know, but is there any reason why tropical filters couldnt have been improvised? They could have asked the RAF to have supplied them with that mod if it was such a problem. It got cold, well yeah Im perfectly aware of that too. The Me109 would have had identical problems to Merlin engined airframes..
Yet the fact is that it didn't. Bf-109's operated without too many problems, though dust filters had to be often fitted. FAF acquired Hurricanes and Buffaloes at the same time, spare supply was cut off at the same time (summer 1941), Hurricanes were almost completely out of service by 1942, Brewsters soldiered on until 1948. Admittably part of the issue was bigger effort put to keep numerically more important Brewsters online, but nevertheless. And the issue was not the fuel, Finns had 100 octane fuel as some other planes required it (Blenheims, most notably).