guys,I just bought a HUD Parking sensor, according to the seller this cool staff display parking distance and vehicle speed on the windscreen, i believe something like reflection onto the windscreen surface, don't know how well this thing works, problem is i have to drill 4 holes into my E34 rear bumper, i m worry this may spoil the bumper, anyone has done this before? i notice there r some round marks on the bumper, shd i drill there? do i have to remove the bumper to get things done? Please advice.thanks.