M keys definitely have a tendency to bind in stabilizer inserts. it's just tolerance stacking. i generally deal with this with dry lubes. for whatever reason, they tend to work really well in this application. the inexpensive blaster PTFE aerosol dry lube is something i've used before to good effect, and i've also used tri-flow dry (a bike lube). the blaster stuff can be hard to get targeted application of, so the tri-flow is probably preferable, as you just put a drop on either the stabilizer insert or the key stem, give it a minute for the light hydrocarbon to evaporate, and then work the key a bit to spread the ptfe particles. this has resolved pretty much every M stabilizer problem i've encountered.
the reason i prefer dry lube is basically because of the vinyl membrane underneath the barrel plate. you really don't want lube sitting on the vinyl and potentially getting between the two membranes.
the only other lube i would use on M stems is possibly very thick krytox (which, to remind folks is basically ptfe particles in filler), applied _extremely lightly_ to the key stems. note that i've never tried this before, and it could turn out to be a total disaster. you have been warned.
