I will be changing my oil in a little under 1,000 miles (about 3.5 weeks of driving for me). I will be using either Techron or Regane to clean out my fuel system. Is there an optimum time/milage to use a fuel system cleaner before an oil change ? I have seen some postings that say that a Fuel System Cleaner should be used about 500 miles before an oil change so that all contaminants "knocked loose" can be flushed out. Whats the straight dope?