The EGR valve oriface in the intake manifold, just behind the throttle unit clogs because oil gets in there, in time and can't really go anywhere. It thickens and becomes a hard gunk-like material and I doubt anything will prevent that from happening (usually takes a long time, high mileage). Keeping the flame trap clean will help but not stop the process.

If want to keep that area as clean as possible (although probably overkill IMO), you could simply do as Ray suggests, remove the throttle base and spray the EGR oriface with carb spray once in a while.