The bearings in the front and rear rollers are sealed and you can't lubricate them. If the bearings are squeaking, you should replace the rollers.
To determine where the squeak is coming from remove the drive belt from the pulley on the front roller and walk on the belt to make the rollers turn. Without the motor noise you can determine where the squeak is coming from.
The reasons the belt will slip after you have tightened it are; the walking belt or walking board are worn or the walking belt needs lubrication.
To check for a worn walking belt or board lift the center of the belt and look at the top of the walking board and the bottom of the walking belt. If either shows signs of wear you should replace the worn part. When you run your hand over the top of the walking board and the bottom of the walking belt they should feel smooth and slick.
To test the walking belt lubrication, do not turn the treadmill motor on. Set the elevation to the highest level. Stand near the front of the walking belt. Push yourself firmly toward the rear of the treadmill. If the belt is properly lubricated the belt will take you to the rear edge of the treadmill and dump you off on the floor. If you move and stop, the belt needs lubricating.
The part number for the belt lubrication kit is 219168. You can buy it at [searspartsdirect.com
]. The cost is around $4.00. The application instructions should be in the package, but in case they are not here is how to apply the lubrication.
Turn the walking belt until the belt seam is along the top of the front roller. Raise the belt on one side in the center of the walking board front to back as high as you can. Apply Â½ the tube of lubrication to the walking board in a zig zag fashion moving from front to back. Move the belt until the seam comes up on top of the rear roller and lift the belt again and put the rest of the lubrication on the walking board in the same manner. Turn the treadmill on and walk on the belt for 10-20 minutes. Walk all over the belt to distribute the lubrication evenly on the walking belt and board.