You can use a helicoil to fix the threads. Basically you drill out the hole to a specific width, take a tap, and then insert a Steel insert that has the threads on it. You can get them at most auto parts stores. Be careful to get out all metal shavings so they don't stay in the oil. Here's a link to the website of the company that makes it.
http://www.emhart.com/products/helicoil.html