Maintenance of off-street parking and loading space. All off-street parking and loading space operated by or associated with a nonconforming use on the date it becomes nonconforming shall be maintained in accordance with all of the specifications of §§ 475-150, 475-151 and 475-153A of Article XVIII, Off-Street Parking and Loading. If, on the date the use becomes nonconforming, it has off-street parking area in excess of that required by these regulations for that permitted use, then the off-street parking area may be reduced to no less than the required amount. If, on the date the use becomes nonconforming, it has less than the required amount of off-street parking required by this chapter for that permitted use, no action shall be taken which will further reduce the area devoted to off-street parking.