Help troubleshooting a transmission issue

[Strider34c]

Hello forum! I am hoping you all can help me trouble shoot a transmission issue. I have a Westerbeke 30b with JS transmission, 2.47:1 ratio. My forward gear doesn't seem to be engaging properly, it seems to have more drive between 1,000-1,200 RPM's than it does at 1,500 or higher. Reverse seems to engage just fine. The issue started about a week ago and has gotten progressively worse. To the point where I can't move forward in calm waters faster than 1.5 knots.

Following the rule of fix the easiest thing first, I flushed the gear box, oil was dirty, but no signs of water intrusion. Ran the engine for 15-20 minutes, working it in and out of gear, changed the oil again, and repeat.

The cable is the right length and moves the arm far enough.

I am a bit if a newb when it comes to this stuff, but am proficient enough when given some instruction. Any help is much appreciated.

What are my next logical steps? I am in Georgetown, Great Exumas if that helps, so not all of the resources in the States.

Thank you all!

[Sailmonkey]

Admittedly I don't know much about the JS gearbox, but it sounds to me like the clutch is shot/slipping. There is no cure for this other than rebuild or replacement (depending on cost of parts).

[bmm32005]

I replaced mine with a Newage, PRM 12.

[Strider34c]

Any particular reason you chose the 120 over the 80? I was told the 80 would handle it just fine and that the 120 was a bit overkill. How was the refit? Did the Westerbeke "kit" make it a relatively easy job? Did you do it in the water or on the hard? Thank you! I am waiting for my parts to ship over and wondering what kind of work it will take me.