This Sight, ML 3in Mortar Mk 2 has never worked for elevation, the mechanism being jammed. Two hours later, I know why. The last time someone took it apart (not I, this is the *first* time I have) they put it together incorrectly, reversing a part. The problem was exacerbated by the dried-out cosmoline freezing the mechanism in the first place. Once I had it moving again, it wouldn't move along it's full legnth-of-travel. Took some puzzling to put it right. That, and keeping track of the...