my new 351 did the same...i built it, and it wasnt my first but sure enough....a drip one night....go a few, a drip....i used the small seal on a new scat crank with no line bore...i'm puttin money on the cap fit/one piece gasket not being happy....usually i just dib some sealer on both sides of the rear main cap in that crack btwn block and cap, then smoosh the tiddy on the gasket in....this time i didnt dib...now my shit leaks