On E39's like mine, the most pointed to failure point is the cooling system - frquently the plastic radiator, the plastic expansion tank, and the original plastic impellers on the water pump.
I had issues with one rear wheel well liner becoming incredibly brittle and disintegrating. It was on the RR where the fuel filler is. I've wondered if the occasional overfilling might have splashed on the plastic and degraded it (from previous owners, of course, lol)
IMO plastic is fine if it's spec'd properly for the application. Just like any type of material.
I had issues with one rear wheel well liner becoming incredibly brittle and disintegrating. It was on the RR where the fuel filler is. I've wondered if the occasional overfilling might have splashed on the plastic and degraded it (from previous owners, of course, lol)
IMO plastic is fine if it's spec'd properly for the application. Just like any type of material.