aluminium stain on waxed beech veneer - how to remove?

Not a lot I suspect. strip sand and repolish

Ok, ta. SS&R would be overkill so I think I'll just cover it up with the light again. (SWMBO isn't bothered. :) I was just hoping someone might know of a solvent I hadn't tried.

Not much. Aluminium is such a nuisance for this that many cabinetmakers don't even use it for saw fences and the like, preferring cast iron. Aluminium-bodied planes were infamous.

If it really is waxed, then you _might_ lighten it by using a wax solvent (acetone is easiest, cyclohexane better, isopropyl alcohol not too good) and plenty of clean kitchen paper towels to scrub the wax off, hopefully lifting the aluminium oxides with it. Then re-wax.

You shouldn't need to re-sand, it only being a surface contamination. It's a pigment, not a dye, so doesn't soak in. Something like a plastic Webrax / 3M pad ought to be powerful enough to lift it mechanically, without creating too much restorative work to the surface afterwards.