Probably one of the best ways to get the tape residue off is to let the piece soak in warm/hot soapy water for a while if you can and then take a sponge to it. Depending on how sticky it is it might take a couple repeats to get it all cleaned off. There may also be some chemical cleaners out there (most likely in an automotive shop) that could do the job faster, but you'd best double check to make sure it won't react badly with the piece itself, as some cleaners are made to be used on metal body panels and are designed to eat away at plastics, acrylics, etc., basically anything non-metal as some are designed to completely strip down to the bare metal to start from scratch. Using such a cleaner on a plastic piece could result in anything from a cloudy/pitted surface, eating holes through it, or completely breaking it down to mush.