Futaba BLS571SV that I was using with RB6 stock just came back from the repair. It took only 4 days from the day I shipped till I get it back! This is what I call the fast great service! Best of all, it was all free of charges except for shipping to the factory.
The servo started rumbling after changing the BEC to 7.4v. Unlike GForce repair which just sent me a new pair of ESC/Motor for the repair in the past, I got my original servo from Futaba. I hope that the servo operates ok.