Toyota Crankshaft Seal
To prevent oil from leaking on the lower section of your engine is the Toyota Crankshaft Seals. They are located at both ends of the cranks shaft where it passes through the engine block.
On the front of the Toyota engine, the crankshaft seal is behind the harmonic balancer. This is the big weighted pulley in the center bottom of the engine. The weights are in place to balance the motion of the crankshaft as it operates. If the crankshaft seal is ruptured in the front, oil will be leaking down from it covering not only the harmonic balancer, but also forming a puddle in the forward area of the vehicle under it. The seal itself might not be seen because of the harmonic balancer is in the way blocking a view of it.
When the rear Toyota crankshaft seal has a rupture, motor oil can be seen leaking off of the joint between the transmission and the engine block on the rear of the motor. The crankshaft seal here can also not be seen by the transmission is covering it. Remember this has to be motor oil that is leaking for the problem to be the crankshaft seal. If the fluid leaking from this joint is red in color, it is the seal in the front of the transmission that is leafing requirement replacement.
In both instances of a leak from the forward or rear seal on the crankshaft there will be a motor oil puddle under the Toyota. An inspection of the upper portion of the Toyota engine should occur before being positive this is the source of your leak, since they are on the bottom, oil could be leaking from above them like from the valve covers.