Its roughly same amount of time to SAFELY suspend the engine and lower the subframe a couple inches as it is to just pull the engine and put the sucker on a stand, which is MUCH safer.
Work your way around the pan on the engine to remove it, don't pick one point to pry heavily at. Take your time.
Get some degreaser and wash that pan. Its easier to work with when its not greasy.
Blow completely dry with an air compressor.
Scrape the sealing surfaces clean with a quality paint scrapper. Take care on the engine to minimize/eliminate debris falling into the block. Be gentle on the aluminum portions at the front and rear of the block. It doesn't have to be perfect, but reasonably close without using a razor is fine.
If the debris falls into the pan, you get to wash it again
You can't use air alone to blow debris out of the crevices between the pan and the baffles within.
If you bend the lip of the oil pan, you must make it square again. Wood surfaces are your friends. I beat all my bent pans square with a 2x4 on a sheet of plywood.
Mentioned above were a few quality sealing products. I've used 'The Right Stuff' without any trouble, its around 20 bucks a bottle.
Since the surfaces are square and pretty clean, you don't need a lot of sealant as too much bleeds out both ways, and you don't want it contaminating your oil.
There is a diagram of how to lay the bead of sealant on this page:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=LU&P=13
Make sure you start all the bolts first without pulling the pan to the block or it will leak.
The edges need to come up evenly for a good seal.
Make 3 passes skipping every other fastener to keep things even.
If you missed it on the link above, you don't tighten the bolts and nuts past 9ft-lbs of torque.
On another note, you have to ask why did the pan not stay sealed? Is it because some uninformed individual used a cork gasket? Is it because you have a lot of crank case pressure? Is it because oil residue was left on the sealing surfaces, compromising the effectiveness of the sealant?