The leak on the back of the engine, passenger side is usually from the timing chain tensioner. It has an o-ring which is the only thing really sealing it. It's a pretty simple fix if you have the basic tools (ratchet, socket) to remove the tensioner, replace the o-ring, and re-install.
The o-ring is available from Toyota.
Re-installing is the trickiest part since you have to keep the tensioner retracted using a clip on it made for the purpose, but if you hit something while putting it in, it will snap and the tensioner will pop out, and you'll have to retract it, clip it, and try again. You also need to rock the timing chain using one of the belt drive pulley bolts, until the tensioner clicks and pops out when re-installed. Sometimes this is best done when replacing the valve cover gasket so you can visually check that the tensioner has popped out. If you start the engine with the tensioner still clicked in, you can snap the timing chain.
Sometimes the valve cover gasket causes leaks on the rear of the engine as well, the combo of an old/original valve cover gasket and old/original tensioner o-ring will usually cause oil leaks, especially at higher mileage.
You may also want to replace the intake manifold gasket on the front of the engine as well. De-greasing the engine beforehand, then popping off the intake manifold, valve cover, and timing tensioner to replace the gaskets and o-ring, cleaning everything up, then properly re-instaling, will fix most of the common leaks, and give a cleaner engine. It'll also be more pleasant to work or or just check things out around the engine bay since you won't have a film of oil on things.