It all depends on the composite. GM used a polypropylene composites for several models in the 90s. And even after 30 years, the panels are fine. They only return back to steel panels because plastics have higher thermal movement so the fits had large gaps and consumers associated plastic as cheap and inferior as the inital dentless marketing wore off in the mid 2k’s.
What your probably refering is ABS composites that manufacturers love using for trim peices. ABS tends to have the stablizers just leech away.
And I’ve owned multiple cars where the plastics just crumbled away. The metal body panels lasted long after.
It all depends on the composite. GM used a polypropylene composites for several models in the 90s. And even after 30 years, the panels are fine. They only return back to steel panels because plastics have higher thermal movement so the fits had large gaps and consumers associated plastic as cheap and inferior as the inital dentless marketing wore off in the mid 2k’s.
What your probably refering is ABS composites that manufacturers love using for trim peices. ABS tends to have the stablizers just leech away.