Customer has just called and it would appear that my van has leaked oil onto their red blocked weave driveway - I didn't realise the van was leaking, and the customer is cross. i have said that I will try and clean it up. What method would be best, as I do not want to cause any other discolouration to the brick when cleaning it. Should I get the customer to sign something that shows he gives me permission to use a "cleaner" of some sort on the drive? Any advice would be appreciated. It is only on one block.