Hi!
I decided to join in with some small tips for the C5.
I don't know for you guys, but my C5 seems to have a lack of torsional stiffness, as at very small speed, every depression on the road makes the doors squeal on the rubber seals. Either the doors or the car, though i'm more inclined for the doors being the guilty part.
So, how do I get past this annoying squealing? Simple: get a bottle of cockpit silicone emulsion.
Apply at will on the door rubbers with a cloth until it's absorved; repeat the process one more time, just to make sure it's nice and well soaked in silicone.
I know that in England, the suns doesn't shine much, but to keep the dashboard from sufering a premature ageing, apply a good coat of the same silicone on it and it will last a bit longer.
The estate's bootlid door has no rubber spacers on it to maintain a good tension on the lock. As such, it may get some play on it; if the door doesn't need to be closed with a strong push, then it's time to fix it.
Just remove the chrome cover along the bootlid opening, slacken a bit the torx screws of the lock, push it around 2mm from it's position towards the rear passengers seat and retighten firmly the screws; put the cover back on it's place and it's done!
It should take 2 strong pushes now to close it.
Take care!