Speedometer reduction ratio gear and housing

[M&A Roadster]

Guys, I need a little help, I've gone through Les Andrew's volume 1 and the trouble shooting guide and can't locate an answer. I just got my 96 year old grandfather's 1928 model A roadster and I'm trying to learn the car and go over it for problems before I start driving it around.
I noticed the speedometer reduction gear housing was split. I ordered a new one with a gasket, when I remove the old housing and pulled the speedometer cable out I dropped the gear. I was not sure which way it was set in the housing, I tryed it both was and it fits with the keyed slot going in from either side. So does that mean it can be set in the housing from either side? The other obvious question is why did the housing split, I'm hopeing that it is something simple like over tightening of the bolts. I looked up at the speedometer drive shaft gear and it looks fine. Thanks