So, I've replaced various parts in this compactor and done various maintenance activities over the years.

About a week ago, it started doing this:

When you turn the start knob, it starts, but immediately stops if you release the start knob at any point. To get a full up-down cycle, you have to hold the start knob to the right continuously.

Now, here's the kicker -- if you turn the switch on the left to 'pack', the ram goes all the way down to the correct pack position without continuing to hold the start knob.

However, when taking the switch off 'pack' and then turning on the start knob, you again have to continue to hold it continuously to get the ram to come up all the way and then release the knob to get the ram/gears to stop cycling and turn off in the correct up position to open the drawer.

Any hints as to what might be happening here/what parts to replace would be greatly appreciated.