What paint to use for water stained hardboard

Hi All
I am trying to sell my house, our large double garage has been lined with hardboard, years ago the roof leaked and has badly stained the hardboard, although the roof was replaced and is 100% OK I think the staining makes prospective purchasers think the roof is still leaking and puts them off.
I have thoughts of painting the hardboard with a cheap gloss paint, do I need a primer, any idears on a source of cheap gloss paint or any other suggestions ?.
TIA
Paul
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How about re-lining it with new hardboard @ 90p (Wickes) for a 4x2 sheet it would probably cost less than the paint, then just seal it with PVA
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