Let's not forget the A4, like almost all gasoline engines of that vintage, uses a carburetor. Carbs need to be stripped down and rebuilt every 5 years in routine use, more often if fuel
has been left in them without stabilant during the off-season. Carbs simply gum up from normal gasoline aging in them (less of a problem since gasoline was generally reformulated by the 90's) and thsat's one advantage of a diesel engine--no carb, fuel
injection system instead. Of course when a diesel FI system has problems, they can be way more of a problem than a simple carb rebuild. Catch-22.