Nobody specific to recommend in your area … but I think whoever you find will charge a lot!
They tend not to replace parts at the smaller level, because their time to fiddle is more than the cost of a larger part. eg, fault = ribbon cable, remedy = replace whole camera and gimbal. …. etc.
I guess step one is to find someone that will give you a quote, at least.
As for SE London, I know there are a couple in London, one in Chertsey area, and one in Brighton. Never used. Google “Mavic Pro Repair”.
Chances are you’ll end up posting to whoever it is. They all seem to be shy of dropping off and face-to-face. So - on that basis, there was a place (in Northumberland) HIGHLY recommended recently.