There's Two things I can think of, methylated spirit my do the trick. The other being Siroflex solvent cleaner. This is used by glazing installers on PVC, if it's as good on aluminium, you may have a winner. Whatever you use will be hard work.
It's not widely known that masking tape does have a 'remove by' time. A lot of the standard tape in DIY stores is only designed for 24 hours. If you need longer, something like Scotch Blue is OK for 14 days.
White spirit should also work fine. Put a clean rag around your finger, dip it in the white spirit and gently rub over the affected area. Do this on a cool day and it should come off with no probs at all. Wash your frames over to remove any residue left behind - job done!
As with all things test a small area first to be sure there's not a bad reaction but tbh it should all be fine.
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