Wheel Bearing Subaru Guide:

Excessive Play

A worn or damaged wheel bearing may cause the wheel to wobble a bit. With the vehicle elevated, check for excessive wheel bearing play by grasping the wheel at the top and bottom, then alternately pushing and pulling at the top. Perform the same procedure by grasping the wheel at the sides.

If you have any doubts about the amount of play present, you should check the lean of axis play at the hub using a dial gauge. Position the gauge against the hub, then attempt to move the hub back and forth toward the vehicle. Rotate the hub to expose any lateral run out variation. The maximum limit of variation acceptable is 0.0020 in. (0.05mm).

Damaged Seals

Closely inspect the seals. Look for any signs of damage, wear or evidence of water or contamination having penetrated the seal. Manually rotate the hub and observe the seal for any oozing of grease, water or dirt. When in doubt, replacement is always best.

Hub Damage

Inspect the hub and races for any signs of damage. Excessive wear, pitting, grooving or corrosion calls for replacement. If you find a problem with one wheel, check the remaining wheels — especially on high-mileage vehicles.