Sun lounger (Crookes S10)

Hi We have this sun lounger going spare - it works fine, we just prefer to sit in chairs when we're in the garden.
I should point out it has a stain on it, (see second photo). I'm not sure what it is, it might be oil I'm afraid. I've tried scrubbing it and it won't come off. However, though it doesn't look nice, the stain does not come off onto your clothes or body!