First are you sure the leaks not comming for above like the oil sending unit???
Second, We used a ball peen hammer to peen all the bolt holes from the inside out,
on all the Ambulance motors we did with tin oil pans on them and they did very well
for years with no leaks. If you have never peened a pan, Just go around all the bolt
holes and give them two or three hard taps so that they are beveled out just a little.
This is done from the inside out, so towards the bolt head. Believe me it works.
Kurt