I have used a BMW cleaning product for removing tar - just wipe it on, wait a couple of minutes and wash it off - removes all sap etc etc.

The worst thing you can do is keep rubbing it, as you have probably discovered. Even when wet, you'll put loads of surface scratches over the car.

Best thing you could do now is to remove it as explained above, then use some T-cut polish (the same colour as the car) to work on the surface scratches you have put in.

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