The actual metal arm is usually not bad, it is the rubber bushings pressed into them that cause the need for replacement. There is a replacement busing kit available but by the time you buy the bushing kit and press adapter/tool you are up on par with the cost of a new arm with new bushings already installed. Pressing out the old, cleaning up and pressing in the new bushings are a PITA. If even 1 of the bushings fights with you in or out, it is a losing scenario, EVEN MORE SO IF YOU ARE PAYING FOR LABOR. From experience we will choose to replace the arm 100% of the time now instead of fighting with the bushings. It sounds like your mechanic also has experience with this, stay the course and the car should be back on the road shortly.