You might not get a warranty repair as you dont get warranty on a warranty repair. If a vehicle is repaired during the warranty period, then the repair is only valid for the remainder of the original warranty period, not another 12 months. As you have taken your vehicle outside the Renault network for service/repair, your warranty is void anyway.
Soz to be the bearer of bad news.
Where is the gearbox leaking oil anyway? Selector shaft or n/s inner driveshaft boot ? These are the common sources of leaks.
Bob