Side covers [Q About Spree - Ed.]

[CharlotteSpreeRider]

I've got several sets of 84 - 86 side panels and several 87 side panels. Are all in deplorable shape, but whatever. The 87 covers are of course much nicer since they include the petcock cover, but they are also made out of a different material. The 84 - 86 covers are very rigid, while the 87 covers are much more flexible. Furthermore, the 84 - 86 covers have on the inside (motor facing portion) a black foam-like crap, or evidence that some such foam-like crap what was once affixed to aforementioned rigid side cover.

This raises some questions.

1. What is the type of plastic on 84 - 86 vs 87, and why was the change made?

2. What is the best way to perform major surgery on panels of each type?

3. What is that black foam-like crap, and what is it for? My only guess is acoustic dampening.

Thank you in advance for any ideas.

[fightingplankton]

i have no valuable input