What Happened To All The Starwar Air Cleaner Bases????

Has anybody else noticed that anytime you see a 67 Starwars air cleaner on ebay there is no metal base or top knob.

Did they use them for Frisbees back then?o No:

Why when you pull a air cleaner wouldn't you take the bottom? And if the top is good how would the bottom get damaged?o No:

Any comments

Thanks
Scott

 

Bottoms Rotted away, have had 3-4 and only had 1 good Base, and 2 of the Knobs.
JR

 

so true...i made one buy dismantling a stock buick air cleaner of that year and engine type and slightly modifying it to fit...vito