I've had quite a few power mirror switches that have worked for only one side or sometimes even a certain direction will work intermittently. In fixing this fairly common problem, I've found that the problem is not always bad corrosion but sometimes loose posts (often E, F, G, and H). Its easy to test this without even taking the switch all the way apart by attempting to wiggle the posts on the back of the switch. I've had quite a few switches where all four posts were loose. A small bit of solder correctly applied while holding the post in position will fix the problem. The contacts should be cleaned though as corrosion can be a concern.
[This message has been edited by GraterFang (edited 04-01-2012).]