Youxin is great for basic CLA services, and shutter work. He’s also cleaned up several lenses for me. Reasonable pricing and reasonable turnaround time.
DAG is for any electronic (the big D) cameras, which Youxin won’t touch. Also, DAG for lens issues requiring collimating, as he has the equipment to do it. And any “special” modifications. He’s so busy, however, so be prepared to wait a long time.
Sherry is a great person (and boy can she talk - if you call, be prepared to spend a little time in the phone!). Does good work, but her quality control is sometimes not the best. But if you have a M5, she’s the best.