There is a TSB that covers this, seems a wrong upper control arm was installed from the factory.
TSB
03-13-5
SUSPENSION - REAR TIRE INNER EDGE WEAR
Publication Date: June 30, 2003
FORD:
2000-2004 FOCUS
ISSUE:
Some vehicles may exhibit rear tire inner edge wear.
ACTION:
If a vehicle exhibits rear inner edge tire wear, and the rear camber reading is beyond the negative end of the specification (max. -2.2 Wagon, -2.3 Sedan & ZX3/5), then install revised +1.0 degree rear Upper Control Arm(s). Refer to the following Service Procedure for details.
SERVICE PROCEDURE
Removal
Remove the rear wheel and tire. For additional information, refer to Workshop Manual Section 204-04.
Remove the outboard upper control arm bolt, and detach the upper control arm from the wheel knuckle.
NOTE: MAKE A NOTE OF THE POSITION OF THE UPPER CONTROL ARM TO AID IN INSTALLATION.
For Wagons only. Remove the lower shock bolt and position the shock aside.
Remove the inboard upper control arm bolt, and remove the arm.
Installation
NOTE: FINAL TORQUING OF THE REAR SUSPENSION COMPONENTS SHOULD BE CARRIED OUT AT OR NEAR THE CURB HEIGHT SETTING. TO ACHIEVE THIS LOAD THE SUSPENSION.
Install upper control arm and a new inboard upper control arm bolt.
For Wagons only. Reposition shock and reinstall the lower shock bolt.
Position the upper control arm in the wheel knuckle and install a new outboard upper control arm bolt.
Reinstall rear wheel and tire.
Recheck alignment to verify camber change, and set toe if necessary.
LABOR OPERATION CLAIMING CHART
Operation Labor Description Vehicle Time
031305A Check Alignment, Replace One Rear Upper Control Arm, And Recheck Alignment (Includes Time To Set Toe If Necessary) Sedan, ZX3/5 1.1 Hrs.
Wagon 1.1 Hrs.
031305B Check Alignment, Replace Both Rear Upper Control Arms, And Recheck Alignment (Includes Time To Set Toe If Necessary) Sedan, ZX3/5 1.4 Hrs.
Wagon 1.5 Hrs.
PART NUMBER PART NAME
3S4Z-1A154-AA Kit - Rear Suspension Upper Arm - Contains Arm And 2 Bolts
OTHER APPLICABLE ARTICLES:
NONE
WARRANTY STATUS:
Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage
DEALER CODING
BASIC PART NO. CONDITION CODE
5500 07
NOTE: The information in Technical Service Bulletins is intended for use by trained, professional technicians with the knowledge, tools, and equipment to do the job properly and safely. It informs these technicians of conditions that may occur on some vehicles, or provides information that could assist in proper vehicle service. The procedures should not be performed by "do-it-yourselfers". Do not assume that a condition described affects your car or truck. Contact a Ford, Lincoln, or Mercury dealership to determine whether the Bulletin applies to your vehicle.