I've diagnosed that the inner-offside (american offside) front parking sensor is dead, so need to replace.

Is it a bumper off job?
Do I need to paint the sensor, I would have thought so but I read a thread where someone suggested they have a plastic cover on them that can be re-used?
What kind of sensor do I need, an L shaped or I shaped one?

You will need to remove the front bumper, and L shaped sensor will fit in all places , they come unpainted, and are available on Ebay about £25 each