Surfing Waves

Hi all,
I have left a board, unused in its storage bag for many years. Board is 20 years old, 7’8” minimalibu.
There are no dings, but I notice that due to heat the bottom has a thin layer of some sort of yellowy brownish gunk on it. I am sure this doesn’t help the board skim the water!
What can I do to bring back the nice sheen?
Would a simple scrub down be enough?
Or do I need to regloss it somehow?
Thanks for any tips
James in HK

Hard to say without first seeing a photo. Usually car polish will work to buff up a fiberglass bottom, but not sure what yours is made out of.

Thanks
I will polish it up.
For now a good scrub seems to have done the work to get rid of the gunk.
Now to repair a nasty hole at the back edge of the board. Must have let it drop on a hard surface.