my screens seem just fine around where I live. Not much dust and gravel in PA....rains too much!

I've had the engine apart a few times and no wear that is any more than anything else. Carbs stay clean too.

One thing that helps is that I don't have a hood scoop. Flat hood. Car runs just fine at the track and gets about 1000miles a year put on. This engine is about 8 years old now.