I don't have any experience with that machine nor did I sleep in a Holiday Inn Express last night but maybe the plastic is what's left of a high-tech plastic (Rulon or the like) anti-friction shim? Put there by the manuf. to reduce ye olde stick-slip issues? Seems plausible to me.
You can probably get the replacement shim for only $15,387.98.
"Accuracy is the sum total of your compensating mistakes."
"The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton