+1
Should have dared them to call the police. If they did, they would likely find out they were in the wrong for trying to detain your vehicle once your bill has been paid. What kind of vehicle is it? There are a small number of vehicles with rather cheap OE front end parts prone to failure at an early age. Torn grease boots do not constitute a safety hazard or out of service order. With non-greaseable joints, it usually means the joint will fail sooner than later, as moisture will collect in it.