There's no way I would use diesel but I am in a very hot climate. I have no idea what climate you live in. Diesel is proven to remove natural insect resistant oils from cattle. Just think of you washing your hands with diesel and then going out into a rain. What's going to happen?
Any solution containing permethrin diluted as prescribed is about the best you can use in my opinion. A mild soap or surfactant (if you have it) seems to help it stick on the cows better. Ensure the soap is mild enough not to take off natural oils providing natural resistance.
I've never seen any pink eye in my cows until this winter. It broke out in totally black brangus cattle. Go figure. This is not a bad fly year either. It is probably my best year in the last 10. 2005 was beyond pitiful and a constant battle.
Our ancestors gave us this. They fought to make it what it is. All we have to do is defend it.