Paragon Transmission 'stuck' in forward

[dwkfym]

I recently delivered a new-to-me P365 back closer to my home waters in the Chesapeake bay.  We had a 150nm offshore passage down the jersey coast.  About 110nm of that was under motor-sail. 

During the cruise, among other things, the transmission stopped getting out of foward.  No neutral or reverse.  Full range of motion at the pedestal lever.  The shifter linkage arm at the transmission was moving when the pedestal lever was moving.  I don't think the clamp at the shifter nub is slipping. 

I am 2 hours away from the boat and I'm unable to go check it, but what are some places that I can start looking to diagnose the issue?  Is there a manual with adjustment procedures?  I don't have the model number off the top of my head, but it appears to be a SOAD transmission.  Sorry for the low-res pic and thank you in advance. 

[SVJourney]

Here's the link for the manual but it  isn't a very good one:  https://pearson365.com/forum/index.php?topic=1938.0

Just 4 bolts to remove the trans cover on top.  Check for shift fork movement inside.  Ensure good oil level  Prolly not an adjustment issue I don't think, but here's another thread with adjustment procedure: https://pearson365.com/forum/index.php?topic=2105.msg10886#msg10886

Good luck!

[dwkfym]

Update - it was just jammed forward due to old oil full of clutch sludge.  I unjammed it by tapping the shift lever (at the transmission) lightly with a rubber mallet then pulling it hard by my hand.  Then did an oil change, adjusted it a bit and its been working flawlessly. 

[dwkfym]

Just updating - my transmission is stuck again.  Engine will start and run in forward.  Same symptoms, except I can't knock it out of gear using a rubber mallet anymore.  Oil looks clean and not sludged up.  I'm 3 hours away from the boat.  I will try backing off the adjustment collar and see if it makes any difference, but I really can't figure out whats wrong. 

I had been using the transmission just fine all season but I ran the engine for about 15 hours.  It seems to get stuck after an extended amount of time. 

On visual inspection the friction plates look fine.  I cannot get any movement from the lever (at the transmission, not at the pedestal).  The set screw at the shaft will slip before that moves.