You will need to pull the washer out from the wall and tilt it back so you can access the bottom, carefull not to scratch the floor. The motor on this washer uses springs to tension the belt on the pullys. Remove the belt. No tools needed. Pull and push the motor forward and backwards and clean out the grooves so the motor moves freely in the grooves it slides on. Spray some silicon spray, armor all or whatever to make it slide back and forth freely. Clean out all the gook, rust, dirt, etc. Now the belt shoud be tensioned enough not to slip.
Larry the Cable Guy(git er done), February 2008