I add one oz of Startron (and 2 oz two cycle oil for lubrication) every tankful. I began two years ago when I had black deposits on the filter. No problems since. I change the filters when they start to get blocked. Haven't changed any since I started the treatment plan.

__________________
Charles
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html