how to do this somewhat depends on what resources you have; If you are doing this on the ground on your back. I would not pull the trans unless you intend to use the 1 piece seal. If you have a lift, trans jack, air tools, etc, then I might just to try and get a better view and more room to work. If you have these resources, pulling the trans isn't a big deal, but if you are on the ground it changes the scenario significantly. Remember that if you pull the trans, the back of the engine has to be supported or it will smash into you firewall; you can pad the valve covers which will make contact (assuming the air cleaner is removed). You need to look at everything on the top side which will be moving when the rear of the engine depresses. I can say that there can be secondary issues unless you take your time; things like kinking the throttle cable, pinching wires, etc. If you brace the engine you should be fine.
as to the leak itself, look closely at the oil pan, specifically the rear lip. I have had a number of issues with this issue; oil pan not sealing. I chased a rear main leak for a friend once and it turned out the pan was the problem; the lip was deformed and oil was passing above and below the seal. Got a new pan, new seal (some RTV) and it sealed up. Another aspect is that of having a good PCV valve; the engine builds internal pressure, it needs to go somewhere; the weakest link in the system will give.
