I use loctite black silicon. just spread it thinly with my finger.
Have sealed about 5-6 RS cam covers this way, never had a single leak, never found any silicon beads in the oil pickups or sump.
did you do it on the rocker cover or the head laine??
You can buy a kit from Renault iirc? whith the correct sealer and a roller
Can the cover be sealed with the cams in place and still in the car?