Johnson Saildrive 15hp gears clacking when in fwd gear

[Lancer28]

I've recently had a problem start up with my saildrive on my cruiser. I have a 15hp 1978 johnson (outboard that seems like it was semi-converted to operate inboard) that is perplexing.

When I am in forward gear (only), it gives a clunk like I put it into gear (I've put it in and out of gear to make sure it is the same sound) at any power setting above 1/3 throttle. I've been nervous of the noise meaning something fatal is on the horizion for this old engine, so I only run it in neutral to charge the batteries. It will cruise along like normal "bzzzzzz", then "CLACK" then back to the normal "bzzzzz" without even a hiccup from the rest of the engine, or power drop.

I've tried holding forward on the shift lever to see if that stops it, as well as using different amounts of forward travel on the control lever to see if there is a cable problem. Neutral is nice and centered on the lever... is that a sign that my control cable is proper and I should start looking deeper?

I'm stumped, where should I start troubleshooting?

Let me add that at the moment, my boat is hauled out, and I am alone, with no "helpers" to assist with anything like a complete pull-out.

Thanks for any help,

Robert

[Lancer28]

oh - I only have 375 hours since major overhaul, so it is not worn too bad...