[Triple-S]

My son treats my V70XC like a truck, and as he's a P & D has splashed gloss down the rear plastic bumper of my car. Thoroughly dry now (doubt it was water-washable) how best should I remove it - I mean would turps or even thinners do any harm to the car?
He has also sat on the leather seat in a paint-splattered overall (!) so I would also appreciate recommendations of how to safely remove it from light-coloured leather.

Thanks for any recommendations (apart from keeping my son from my car....)

P