How can I repair my Proform treadmill?

1) The belt is not remaining centered and sways to one side (the right) when in use. 2) The speed of the treadmill is constant as per the display until I start walking on it. The belt then begins to drag and the display speed decreases. I then get off the treadmill and the speed increases significantly and an E3 error is displayed on the console. The treadmill is several years old and I have misplaced the owner's manual. How does one adjust the belt? Is it possible the treadmill needs lubrication? If so, what is the best lubricant to use?