If the plastic got yellowed from smoke, that may very well
work, but if it got yellowed from UV sunlight, nothing
short of sanding down the plastic will rid the yellowing.
I tried restoring several Amiga, C64C and Atari cases
to no avail. They all suffered from UV damage most
likely direct sunlight over the years...
Ever notice like on A4000's that certain parts of it will
yellow more than others? I also have a C=1902 that is
fine but the door is yellowed! On my A4000 all is fine
except for the plate under the floppy! Some plastics
yellow more than others.
Tim