Having a gripper diff will make next to no difference for a service. You'll just be advised to use slightly better oil than the standard renault stuff if anything.
So if you don't want to or can't do it yourself. Any Renault specialist would be fine. To be fair any general mechanic will be able to do any service stuff you want too, just make sure a good gearbox oil is being used. I use Fuchs Titan Race SYNCHRO 75W-90 but Redline comes with the best recommendation,