This sour smell is most likely the monomer methyl methacrylate (MMA), which is sometimes trapped in small quantities in the polymer in the polymerization (plastic-making) process, but should also be a product of long-term photo-degradation. I'm not sure if you could stabilize a Lucite product. However, if it is MMA, it could be washed off the surface with ethanol (alcohol) or perhaps even hot soapy water, without dissolving the Lucite. Acetone should *NOT* be used-- it will dissolve the Lucite and etch the surface!
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