Port Engine Prop Turns when in Neutral

[Jaskson123]

I have 1990 twin 454 Cruisaders, My port prop turns when in Neutral. The boat is out of the water for the Winter and unable to turn the prop manually by hand in either direction. My starboard prop turns easily by hand.
Where should I start? Hoping this is not a huge issue

 

[bondo]

Ayuh,....... What transmission,..??

 

[makomark]

I'd bet it has a BW 72 series gear and the clutch plates are warped....for starters...