Larry,

Changing Delvac at 500 miles would be very expensive at ~$5 a quart.

As you probably know, I change oil at 10,000 miles and use Rotella, Mobil! or Castrol synthetic oils. I also use Gunk engine flush when I change the oil and filters. The flush is in the engine for about 10 minutes then drained with the oil

Recently I had the valve cover off to adjust the valves and there was not a trace of sludge on the head or on any of the valve mechanism. This engine has 250,000 miles and if any sludge was forming, there would be some there by now or maybe its just cleaned away by the engine oil and flush.

P E H