70 bucket seat plastic

[3macs1]

Hi Donnie:
I have it all , in fact two or three times over but there is a problem with it . There is something wrong with the plastic composition in my mind right from the factory with this color. Being up North the cars rusted out but with no heat the interior pieces are the best you will find all expect this color for some reason.I parted 3 70/71's with what I will call white interior.To me the 70 stuff is parchmant and the 71 ivory but I am no expert. All of the plastic pieces on the side of the buckets, the rear and front arm rests etc have like a white chalky dust on them and when you rub the plastic it breaks down right in your fingers. The black pieces put away the same time in the same box are mint.
My brother went through this also with the white interior in his impala and ended up using repo which was not what he wanted to do but we could not get the originals to stop breaking down. We tried cleaning first then repainting and nothing seemed to work.
Is this something common and can it be fixed so these items are usable??