I have a 2001 C Class and I have just purchased a private number plate, however I cannot get the rear plate screws off. The top ones came off no problem, however the bottom two will just not move. I sprayed some WD40 on them and one of them started moving but it does not unscrew, it just keeps going round and round. The other one still will not move and now the screw head is starting to give way. Help!