Hey guy's it's very simple... ... ... use a new sealing washer with every oil change, or in the case of the newer trucks, a new drain bolt with built-in sealing surface.
Yes it might cost you a little, but thats the price of ownership. The drain bolt on the newer trucks was never meant to be re-used, it is a one time throw-away piece. Same goes for the sealing washer on the older trucks, use it once and toss in the garbage with the used oil filter. Also, the drain bolts should be replaced on the older trucks every other oil change. You torque them down, just like a head bolt, which results in "stretching" the bolt. Repeated use will weaken the bolt and keep it from retaining it's torque setting.
Like most people, when you noticed the leak, you tried to re-tighten the drain bolt, but that didn't work. Of-coarse not, you have a sealing problem, not a torque retention problem. This is just how 100's of owners strip-out there oil pans every year. Question??? What cost more over the life of your truck, a few drain bolts and or sealing washers or one new oil drain pan??? The answer is A. a few drain bolts.
If you would like a place that stocks new drain bolts and sealing washers, along with optional Magnetic drain bolts for that little extra protection, try ProWeld Performance Parts. They sell drain bolts and any filter application you could ever want (air,fuel,transmission,cabin air) along with L. E. D lights, Wire and Cable, Electronic supplies, ETC. Mention you are a TDR member and receive 10% off your next order, along with a free oil filter for your truck.
Check the manual for the correct torque settings, many publications I have seen use 40 ft/lb as the drain bolt torque setting, but check for your particular engine.
www.proweldperformanceparts.com
Attention: TDR Forum Junkies 
the correct spec was in the forties. 
