Cooler is rebuilt. The o-rings weren't even rubber any more. Brittle and hard as a rock. I didnt have to cut them off they just fell apart when I touched them. Cleaned the cooler and header mounts with carb cleaner and a wire brush. I used small floor jack with a folded towel on the plate and pressed the front header in using the frame of my truck and another towel at the top to be safe. I had removed my lower rad. hose to get the cooler out and made the mistake of putting the hose on before re-installing the cooler (waiting for the o rings to arrive). I had to remove the hose a second time and the factory clamp at the top is not easy to work with so for anyone doing this its best to leave the lower hose off while re-installing the cooler. Bolted in the front header with gasket then used alot of colorful words, prybar, small 2x4, and lots of muscle to get the front header on then bolted up with the gasket. Changed my oil and started the flushing process. One flush down starting on 2 and 3 tonight. I did flush the radiator first with the hoses unhooked. I used hot water and prestone flush solution. The coolant that gets mixed with the oil (sitting for weeks) coagulates the motor oil and makes life harder in this instance. It is best I would think to flush your system asap. I will be changing my hoses probably another 2 times to play it safe as well. Would like to thank everyone for their input on this. I was first shopping for new motors and now I am back in action and my son is very excited to ride in daddys truck!