Maybe a dumb suggestion because I'm having a hard time visualizing the problem. But couldn't you insert a thin "star" washer, or split lock washer between the plastic insulator and the chassis? Maybe the "teeth" would dig in and stop the thing from rotating.
Yes it's a shame that you have to come up with fixes like this on your own. And Yes, Lionel does sometimes make wholesale changes to what looks like the same product. The Legacy E6 (Pennsy-style) 4-4-2s have been made at least three times. The first one, Santa Fe 6-11117 , had captive axles. The next batch like my 6-11232 B&O had removable axles and a "bottom plate." Bravo! Then, based on Forum members' photos of the latest 6-84942, it LOOKS like Lionel went back to a one-piece chassis. I don't believe the exploded parts photo posted on the support website is correct for the latest release! Since the production runs are done by possibly different contractors in China, it's like a box of chocolates. Until Alex, Pete, or GRJ takes one apart, you never know what you're gonna get!
I'm with Soo Line, not pre-ordering ANYTHING. I'll take my chances and pay a premium to a greedy hoarder or collector, only AFTER the Forum gives the loco it's blessing 
