Ice maker overflows, replacing valve didn't help

I would appreciate some help diagnosing a tricky fridge problem. I recently moved into a new place with a several years old GTS18SHSVRSS. When I moved in the ice maker was fine but the water filter was stuck and the water dispenser spout inside the unit wasn't working. I unstuck and replaced the water filter (the previous occupant of the house hadn't changed the A/C filter so safe to assume the water filter was due as well) and the water spout started working, but the ice maker began to overflow. This was a constant overflow, not just a half a cup per cycle like you'd get if the ice cube size needed to be adjusted. I replaced the water valve, which didn't help. I also took out the ice maker, let it thaw overnight in case something was frozen up, and then screwed the cube size adjustment all the way down before reinstalling, and the sucker still leaks. The only wildcard here is that this is on the top floor of an apartment building so the water pressure is adequate but not awesome, though the ice maker apparently worked for years before I moved in so who knows.

I'm guessing I'm due for either a new ice maker or a new circuit board, but I can't find the boards online. Figured I'd check in here before I called a repair tech -- anyone got any ideas?

Thanks!