Hi Dony
Had the same problem as yours. If you lift up the boot liner on the right hand side and look for the black or white plastic vent you will probably find that this is where the water is getting in. The best way to check is to use a hose pipe and direct water over the joint where the bumper meets the rear wing. You should notice a small trickle of water coming from the outside of the vent. I just got some silicone sealant and sealed all the way round the outside.I've not had a problem since.HTH, Moody.