I'm new to Renaults so this is my first proper post
I wanted to add my 2p as I always seem to end up with cars that need work. Hopefully my Lag wont be one of them any time soon.
For really stuck bolts try tightening just a few degrees with a long breaker bar, then loosen.
But be careful - there is nothing worse than shearing off a bolt.
A nut splitter can be handy where there is space but so often its bolts that are stuck. My solution is to arc weld the top of the bolt. This puts concentrated heat directly into the offending thread.
But arc welding can be harmful to the electrics
# Disconnect the battery
# Disconnect the engine
# Put the earth clamp close to the work area.
If a ball joint nut keeps spinning either split the nut or try to get some fine grinding paste into the taper and hold it together with a G clamp. The nut should then unscrew. If you go for nut splitting you have to go the whole way. The nut will compress onto the threads and be impossible to turn if you give up half done.