Like Rob said there’s no mechanical drive like a manual transmission. Most of these hydrostatic units have a master pump that transfers fluid under high pressure to a slave. They resemble the cylinder of a revolver. Many times fresh (oil) and cleaning the intake screen will resurrect a problematic transaxle.

dont feel too bad guy, I had a sudden drive loss and also overlooked the air purge procedure. decided to tear the hydro down, only to find everything in perfect working condition, this of course was several years ago but I'm assuming this was also your motivation for your teardown....yea Robs right, your trans should work just fine after adding fluid and running through purge procedure. Otherwise, very descriptive video buddy.

Pulley drives the hydraulic pump. The hydraulic fluid drives the hydraulic motor. There is no mechanical connection between the input pulley and the axles. The hydraulic fluid transfers the torque

You don't seem to know what your doing.