Olympus E520 Focus problem

I have two Olympus E520, and Both have problems with focus at large apertures and large focal distances (for example, shooting at f3.5 at an object 40 feet away). The images almost always were very soft, but if I shoot the same image using Live View and Contrast Detect AF, the image was SHARP. I have an E510 too, and in this cam with the same lens, the pictures always was sharp using Sensor AF (viewfinder).
This happens with my lenses: 14-42, 14-54, 40-150 f3.5-4.5, 40-150 f4-5.6.
If I close the aperure to f8 in the E520, the images improves, but with my E510 I can shoot the 14-54 wide open without any problem.
I live in Venezuela, so sending my two E520 to USA for warranty or service (I buy them in Amazon by Internet), is a pain to me. If you can tell me how to adjust the AF mirror to compensate for front or back focus, I will apreciate so much.
THANKS.