Okay, I've been trying to decipher the ALPS part numbers. This is the one listed on the parts list:

EC11E15244C0

This exact model number still seems to be available at some suppliers. ALPS, however, does not list it. They list models with the two last digits different. I thought that might just be a batch number, but they currently offer two EC11E15244 models with different end numbers. The difference between them is the travel of the push action, G1 == 0.5mm and B2 == 1.5mm.

EC seems to mean "encoder". 11 seems to refer to the size of the switch body in millimeters. E may refer to the torque rating and/or operating life. 15 seems to be the number of pulses. 2 seems to refer to the number of detents as multiples of pulses. (It actually seems to only ever be 2 or 3, with 3 being detentless.) 4 seems to refer to the travel of the push button mechanism (0 == none, 4 == 0.5mm and sometimes 1.5mm, 5 == 1.5mm). The next 4 seems to refer to operating life. (Seems like higher is relatively more within the same class.) The last two, I'm still not sure.

That's a through-hole unit. The surface-mount units seem to be the same except J instead of E. There are also through-hole units that are K instead of E, and they seem to have longer lifespans, mostly.

I'm inclined to get a longer-lifespan unit to see if it still works. I'd rather only have to do this once.