Honestly I wouldn't worry about this too much. While it's true that the M0131 might have been discontinued fairly early in the production life of the Plus it is arguably the "correct" drive (from an aesthetic standpoint; the later drive has that extraneous-on-a-mac eject button) to go with it, and even if was discontinued the day the A9M0106 came out (to accompany the IIgs) it's perfectly feasible to imagine that someone buying a Mac Plus in 1987 might end up with an old stock one. One came with my Mac Plus, which I *think* is Platinum cased, although it's so yellowed I can't say for sure.This one will probably end up primarily being used on my Mac Plus once I get its display working again. Trying to get everything era-appropriate as possible.
If I were setting up a Plus "museum exhibit" I'd definitely go with a M0131 given the choice.
