But trust me, at the same age, M's and F's will be similarly brittle. Getting the plate off an '87 3151 is harrowing because it's pretty much guaranteed to break the post.
Maybe I have just had coincidental experiences with different batches of plastics, but I have owned 10-12 Fs and at least twice that many Ms, and the difference in the cases is night and day.
I have never broken an M case or received one broken in any way. I dearly love the F but the fragile cases are atrocious.
The M plastic just seems very leathery and tough, while well over half, if not 2/3 of the Fs have had serious damage before they even got to me, usually cracks radiating out from inside corners and that surface layer peeling off.
I am terrified of opening up an F AT because of the way the shells clip together at the front. At least the other Fs have metal backs.
Well, statement stands, and is true. The reason the F's break so much easier is because the shell is so different structurally. Same plastic, just less of it and shaped in a way that's not as sturdy. The M's got more reinforcing ribs, certain vulnerable areas are thicker and so on. Basically, the F was designed as a piece to be thrown on over something sturdy whereas the M was designed as being the sturdy element. End result is that the F is 'just a shell' whereas the M is an actual chassis.
Hence why I basically defecate building materials when it's time to rebuild or clean an '87 or '88 M. The brittleness is nasty enough in the M that
because it's a structural element and anchor point, the posts just
love to shatter at the slightest hitch. No surprise, it's most evident where there's the least texture as well. (Going back to the manufacturing process and mold as an element of the problem.)
For maximum wet yourself with terror, try rebuilding an M5-1. Not a -2, a -1. The trackball mount is mounted with self-threading screws or clips, depending, and is very thin ABS. It's even more terrifying than dropping the upper shell of an M13. And it HAS to come out to clean the optical sensors. So much
fun... ;P