Question about oil leaks

Visiting from the GM forums (excuse me), working on a 2000 DOHC Corolla. There appears to be a substantial oil leak rear of engine r/s running down above the p/s pump. Any common issues with this. It still seems that even this leak would not account for 300 miles to a qt. 107k mileage, well maintained. Not the valve cover gasket or plug tube seals. Thanks guys. Shep

By no means an expert, but I believe sometimes oil can leak INSIDE the engine. How does the radiator overflow bottle look? If it has a film of 'gunk' near the top of the bottle, you may have oil in the water system.

Timing chain tensioner o-ring