Hi guys,
thank you all for your input. Unfortunately I can't replace anything bcz I don't have any spare parts. Yet, I discovered another thing, I connect the receiver battery to the receiver, turned-off the ESC and removed the main battery pack so now the servo is running on the receiver's battery. I got a screwdriver and started touching it on the motor- mind you again no power to the motor, every time I did that the servo glitched.
Does that give you any clue?