Removing the back cover won't tell you much.
I suspect the issue is the input shaft coupler and pins that secure it to the driveshaft.
Broken spirol pins in the driveshaft coupler........
Remove the tunnel cover to access the coupler for inspection.
Remove and inspect the pins and coupler and mounting holes on the driveshaft proper, repair/replace if necessary.
Support the driveshaft while driving out and installing these pins to avoid damage to the bearing in the transmission.
Use the proper roll pin punch
Look for wallowed out holes in both parts. Therein may be the issue causing the pin(s) to shear.
Be sure and use NEW spirol coiled pins and not the hardware store split ones.
If you can remove both pins, you might be able to raise the shaft enough to remove the coupler.
If not, the engine will have to be slid ahead in the frame so the driveshaft ass'y can be removed.
https://www.cubcadet.com/en_US/conte...670a0f800d1a/y
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