personally, i have never had probs with oil leaks but thats due to double checking gaskets and bolt/nut tightness before final "drive out".
lots of people who build cars in garages/back yards i have noticed have a "thats good enough" theory!!!!!!
and clearly, "thats good enough" is nowhere near good enough!!!!!!!!!!!!!!!
most home builds i have seen are shocking but thats another story lol
Sean.