As GTB above has stated, other leak sources can prevail but sometimes the front corners leak where the pan and the front cover meet and the road draft will carry the
oil along the pan rail and collect at the rear. The seam on an
oil filter can leak. Another spot to check is the lower rear corners of the valve covers, and rear most edge of the intake manifold. Good assembly practices with good sealants will minimize this annoying condition. A product to check out is called "The Right Stuff" it is made by Permatex and comes in a small aerosol can like "Cheeze Whiz". It is far superior to silicone for preventing
oil leaks. It does not "Flow" like silicone does and has some very good binders in it, allowing it to bite into irregular surfaces much better than silicone. It's a little pricey but well worth investigating.
Good luck.