There are numerous places for leaks to occur. Gear selector shaft, dipstick tube housing, k/down cable, speedo housing, etc.
Sounds like you are pretty sure it is the oil pan or mounting. Check the pan for porosity, fill it with kero or metho [ don't drink the metho afterwards...].
If no leaks, back to square one....
You correctly snugged the bolts, the right thing to do. Problem is snugged is not tight, but you cannot over tighten with cork/rubber because you squeeze the gasket out...& cause a leak. The other problem with snugged, not being tight, is that it can loosen...& does. If the pan is ok & you are sure it is the gasket not sealing, use silicon with no gasket, as I suggested & it will NEVER leak. Run the silicon around the inside of the bolt holes, close to the holes to make sure it seals with the case. Apply the silicon the case & make sure the pan covers that area. To make it easier, buy a length of 5/16" Whitworth or UNC rod threaded rod from Bunnings. Cut two lengths about 3" long. Thread each one a few turns into the case, diagonally from each other. Do this first, apply the silicon last as it goes off in 10-15 min, so have all the tools ready. Use the rods to guide the pan into place & not get silicon everywhere.