Would one that was made in the early 90'S 92fs have plastic parts
No, it would not. Around the early 2000s is when the plastic/plastic coated metal parts began showing up.
In truth, there is nothing wrong with them at all as far as function goes. Some even say they can be
better and more reliable over the all steel parts. For example the plastic guide rod has slots in it and by nature of it also being plastic, can flex to allow things like sand or dirt to not get clogged so easily along the sides of it.
For me PERSONALLY, I like the steel parts better. They just feel better, especially the trigger and magazine release. The slide also seems to move a bit easier with a steel guide rod and the gun balances better with one in as I like a bit more of a muzzle heavy feel. It also makes the gun feel a bit higher quality and like the classic M9s I used in the service.
And as for Check-Mate magazines, not all of them are bad for the M9. Pre-2005 magazines had government-specced heavy parkerization on the inside and outside of the magazine. This caused Iraqi sand and dirt to really embed itself inside, tying up the follower, jamming the gun. Once this problem was realized it was too late but Check-Mate changed their specs and any post-2005 Check-Mates lack this heavy inside phosphate coating and are reliable and pretty good magazines, being slick and smooth. I own several for my M9 and they work great, as they do for many people. You can get them new in wrapper and they are G2G, much better than old used worn out and tired USGI mags.
I'm off to the range this morning to put a couple hundred through my M9.