We have an engine builder near here that has a huge belt sander, he ran my 230 manifold over the sander for about a minute and it was great. But don't forget, if you have a fresh engine most likely you didn't re-torque your manifold at about 500 miles, just try a new gasket and re-toque every couple hundred miles until the nuts don't move anymore. Also check oil pan and side cover bolts. I make a bolt check on the whole engine every spring when I get the truck out, there are always a couple a little loose.
