trek shows that both the 412 and 414 were offered in those "m" serial number years, '80-'82, in this slate color. and, unlike other models, the "m" serial doesn't designate year. so, i'm guessing '80 with the late '70s derailleurs. but, if those aren't original, i guess it could be one of the other two years as well.

regardless, it's odd the frame doesn't have brazed top tube cable guides. but i think it's prettier this way.

trek shows the 410 model as only available in one year, '85.

thanks!