What direction is the slippage? This can help diagnose the exact reason.

It slips when moving towards the front, so the prints always end up shifting towards the back of the machine at various points.

I would dissemble the whole thing but it is technically my company's and they are frustrated how much time and effort this thing has taken to get to work properly...

For my Y axis remount, I pressed down on it with 1 finger to tension the belt as I tightened the mounting bolts.

I removed my Y motor from the doodle, Held the motor in my hand and pinched the gear collar (what is that thing actually called?) between my fingers and tried to move it with the manual control.

I had used a fine point Sparpie to mark the shaft/collar. The attached pic is the result.

If the collar does not slip on the motor shaft, is the shaft itself slipping or is it the belt slipping?

Have you swapped the motors around?

The machine went from occasional (and extremely annoying) slippage on the y-axis to simply being now completely unusable.  It's gotten progressively worse, even as I've attempted to fiddle with how tight the horribly small little screw bolts are that anchor the bearings to the rod for the y-axis on my 3rd gen solidoodle.  I've gotten maybe a couple actual usable prints out of it before it just simply decided it wouldn't have any more of it.  The entire print head assembly (with the x-axis rods) will literally now "bend" and contort as I adjust the y-axis amount.  If I tighten the bolt screws any tighter for the y-axis the motor itself will grind.  Not tight enough and it just slips.

The machine isn't usable at all anymore so I suspect I'll have to do a complete teardown of the thing in order to fix whatever is happening here.  I'm going to try a bunch of white lithium grease on the rods as a throwaway effort but does anyone else have suggestions?

What direction is the slippage? This can help diagnose the exact reason.

For me, cooling the electronics on the back is a must. I can't print without a fan on it.

Yeah, right now I've got the unit directly in front of an ac unit so it's definitely very cold at the point of the electronics.  Cooling shouldn't be an issue right now, it really does look more to do directly with the y-axis hardware (rods/bearings/grease/belts/etc.)

The machine isn't usable at all anymore so I suspect I'll have to do a complete teardown of the thing in order to fix whatever is happening here.  I'm going to try a bunch of white lithium grease on the rods as a throwaway effort but does anyone else have suggestions?