Cleaning up hardwood

[Michael Rogers]

After about seven seasons protected by 'Seacoat' - now apparently defunct as I have beefed about previously - the seat slats in Cavatina need sanding and recoating.

Ingress of water/salt/whatever through tiny dints in places has left the affected wood 'stained' in unsightly spots. Apart from attempting to sand them off (doesn't always work), is there anything one can apply to help remove these marks before re-coating? Is this oxalic acid territory?

Michael R   (Trouper 12 'Cavatina')