Saving Old Seagulls

I have a 78-79 40 plus longshaft with a clutch
I've been using it for a couple years now, great motor
I replaced one of the bottom end seals(the one behind the prop) as it seemed to be leaking it's oil
I couldn't get at the top seal.
Anywho a few weeks back I'm going on a camping trip and the motor was starting to make more noise than usual (rackety rackety)and vibrating a little more.
As there was no wind and my little sailboat is pretty heavy annnd we were close to our destination I kept on
We had a couple of big powerboats go by and as a result we nosed into a big wake, the motor starting revving like crazy and we stopped making any headway.
After we paddled to the dock I checked it out(took it apart) and the clutch was not engaging the prop.fully, just a little thus the noise I guess
There is some wear on the corners of the unit that engages with the drive shaft when the fork lifts, but I can't really see what the problem is
Any ideas? Could it be the spring which pushes it together??

suggestion:
remove the gearbox end cap (the one with the drain plug) remove the prop/spring and push the drive shaft out towards the rear.
clean everything inside the gearbox.
i bet there's a lot of crud inside it (dried up gear oil and salt deposits etc which might be preventing smooth operation of the clutch)
the drive shaft itself has to move in and out to seperate the 2 gears and if there is a lot of gunge and congealed mess it'll be stiff in both directions hence either not very well engaged/slipping or difficult to disengage. (does that make sense?)

basically a strip and rebuild job.
fresh gear oil (depending on which gearbox you have) probably ep90 or similar and then just keep the gearbox topped up with gear oil every time you use it and it should be fine. from memory, every ten hours of use the gear oil needs replacing.
LOTS of seagulls dont even get this from one year to the next. hence very worn or broken gearboxes?
much cheaper to replace oil than gears.

I have one just like yours....I will be going trough it this winter.....have a service manual....hopefully it will help

Yeap, check the condition of the spring inside the gearbox, clutch dog and crown wheel. You will get the answer inside the gearbox.