There is a fault associated with the auto transmission and the warning light is indicating as such when it comes on. The fact that loses power suggests that it is going into limp home mode, which is designed to give you enough power to drive on to a mechanic or dealer. That it isn't on when the mechanic checks it says that it is an intermittent fault, which can be hard to trace. I would take the car to a Renault specialist and have them check it.

Renault's offer is standard practice within the industry. The amount they pay is based on the age of the car, and the use you have had of the failed part until it broke. What they are saying is that they can't fit a part that is four years or so old and done 100,000 km or whatever your car has done, and by fitting a brand new part they are returning the car to new condition. In effect you are being asked to pay for the use you have had of the old part. It might be frustrating, but it's as good a deal as you are likely to get and I would go for it. The alternative, if you're up for a fight, is to seek advice from Victorian Consumer Appeals Tribunal (VCAT).

It really comes down to what you are comfortable with. Renault does send its mechanics and technicians overseas for factory training so they should be armed with knowledge to fix whatever problems owners have, but you do pay a price for that. My advice would be to use the dealer while the new car warranty is current, but then switch to a reputable mechanic after that, one that preferably has knowledge of Renaults.