My wife's camry began dripping oil excessively when parked. The issue turned out to be the "spaghetti seal" : an o - ring around the oil pump cover. While I was in there, I changed the timing belt. The documentation is easy to find on how to get this.
The two things that made this job tough:
1) the bolt that holds the crankshaft pully on is torqued to about 10000 foot pounds. The large breaker bar did not work. The air powered impact wrench I bought did not work. Some people have said they wedge the breaker bar on the floor, and then "bump" the starter to get the bolt loose; I didn't try that.
Ultimately I heated the bolt and the pulley with a torch for about five minutes and that got it loose enough to get it off with the breaker bar.
2) If you mark the timing belt when you put the new one on, and then rotate the engine a few times, don't expect the marks on the belt to line up with those on the gears again. That doesn't mean the belt skipped. The gears and the belt rotate differently, so that the same spot on the belt does not line up with the same spot on the gears for a long time! (many rotations)
This caused me a good bit of consternation; I kept thinking the belt was slipping.
You have to make sure the timing marks on the gears line up properly after a couple of rotations, but don't use the ones on the belt except the first time, when you put the belt on. With each rotation those marks fall on different places on the gears. Here is a picture of the leaky area around the oil pump.