Three primary things I look for - warpage, damage from previous over-tightening, and early/late pan rail style. All three cause leaks. If I check all three and make the corrections that are almost always needed, I rarely have pan leaks. The fourth is over-tightening, and I only use light even torque (fingers and thumb on a ratchet head or driver) to avoid making new leaks. This way you can tweak a bit tighter if necessary - but I rarely find it's needed.
Warpage is simple. Place the pan upside down on a very flat surface. If it rocks, it needs work. Placing a bright flashlight under it and turning-off the room lights will show low spots and minor warping. Warped pans (not low spots) can be tough to repair, with a twist one way fixing the original warp and causing another, but placing a wedge under one point that's contacting the surface and applying pressure can get it with care.
Low spots found with the light, a straightedge, or block/disc sanding can be worked-out with body tools. Often the low spots are actually caused by over-tightening that raises the metal around the bolt holes. A combination of leveling the holes and raising the rail in-between works.
Finally, be aware there are two basic styles of small block pans and gaskets - two-piece and one-piece. The older pans (pre-1986) have sharper corners at the timing cover/oil pan and rear main corners for cut gaskets. The later pans have a larger radius to use one-piece steel-core rubber gaskets. The clue is if the gasket has a relief cutout for a block dipstick ('86+), it will likely leak with an earlier pan type. Most of the cheaper "one size fits all" are this type and need silicone. You can get one-piece gaskets for the older pans, but it must specify that type. The timing cover corners are always the same, it's the oil pan that is different.
I have found the Ford and FMS 1-piece types do not leak when installed dry with a straight pan of the correct type, but be aware Ford used silicone in the corners on production engines.
There are other issues with timing covers and seals, but I'm not sure if that was part of the discussion. HTH
David
Even new, stamped steel pans are not perfect. Note the dark areas in the pan rails below, indicating I need to do a bit more straightening with the hammer and dolly:
