hi,
just started on my 81 kdx plastics and needed to remove the chalky oxide of plastic on the rear in particular.
l saw the scraper method and other than looking a bit tedious, it left flat sort of marks on it.
Having detailed plenty of cars over the years and having that sort of stuff in the shed l started off with a fairly fine steel wool and washing powder in hot water to get the worst of it off.
Then went to paint cutters by hand, that got things smooth though dull,good for getting into the corners where the steel wool missed.
Next to a fine hand polish and finished of with the buff in the vice with a wool pad and very gentle buffing as not to burn or melt the plastic
Maybe an hour each if that.
The tank , l started to buff it with a wool pad and polish, havent finished that yet but the bit l did looked good.