You don***8217;t actually say if you have just bought the car? Unfortunately you must do your home work when buying second hand cars and checking the service record is important. No doubts one of the reasons for previous owners selling a car is wanting to avoid the expense of having the cam belt replaced.
The cam belt service interval is 5 years or 72,000 which ever comes first on the 2.0 Scenic.
Service interval for cam belts vary widely between cars and car manufacturers for instance on some Renault diesels the service interval can be 5 years and 45,000 miles. So I would say an independent garage who see a wide range of cars can be forgiven on not knowing all the specific serviceable data for each individual car they see every day.
I have recently changed a cam belt kit on a 2.0 Scenic the car had done 130,000 miles and was on it's second belt so was under on the mileage for it's third belt but as the last one had been changed back in 2004 was almost 2 years overdue on time. On removing the cam belt cover I was greeted with this sight a split cam belt roller guide which clearly was about to disintegrate at any time which would have caused the cam belt to lose it***8217;s tension and have the same effect as the belt snapping. The engine timing is lost and the valves then collide with the pistons.
Here is a cam belt and guide rollers on a 2.0 Sceic that had done 65,000 miles and was several years past the time service intervals
This caused all the engine valves to get bent even the ones in the back back ground are bent
Though fourtunatley on these engines the valve stems are relativley weak so bend readily out of the way causing little other damage.
I have also repaired another 2.0 Scenic with cam belt failure with only 55,000 but at 7 years old was 2 years over due a cam belt change.
I have just repaired yet another 1.4 16 valve Scenic with cambelt failure 03 reg never had a belt change with 100,000 miles on the clock so had been really runing on borrowed time which a garage had quoted £900 to repair. I bought non OEM parts to repair the engine for under £200 but it took me several days to complete the job.
I think £2000 sounds rather a lot to repair one of these 16 valve renault engines with cam belt failure though even if all the valves where bent.
I don't belive any of the above can be called design failures rubber degrades over time and bearings wear out and plastic rollers can become hard and brittle and break.
All the above IMO are all down to lack of servicing and the owners responsibilty.