I've often spoiled the lovely brown patina of a tuner shield when someone else's chassis was on the bench. Ever wonder how the 10-20 years of accumulation got there? Two smokers
dust, dog dander, and lest we forget pan-fried meat most mornings and evenings!
What was most annoying was the little grease-impregnated sponge inside Magnavox shields. The sponge would disintegrate over time, and the tuner would need a massive hosedown with Blue Shower to get the stuff out!