Tom sorry to hear about your oil problem i see it's been awhile since your last post. Not sure if you got it figured out yet or not. If it takes a while for the oil to show up in your Rad it probably your injector cups. What happens is oil sit on top of the head around the cup and as the coolant system cools it make a vacuum pulling oil into the coolant. Isuzu had a problem with that era engine because they only had one O ring on the cup. They updated the heads and cups i believe in 2006. I hope this helps. Not a a real big job to do if you have the tools