The gearboxes are fairly straight forward.(that big spring should last for ages as long as there's plenty of oil around it)
The operation of the clutch will depend on how much corrosion there is around all the workings. Simple stuff once you've worked out what needs doing.
It's the engine that probably suffers more with corrosion, especially after saltwater usage and then a total lack of tlc afterwards. It's the salt that does all the damage to the cast iron, and if you're unlucky will split the block if it's been left unattended for years on end. That's why we keep on about flushing the motor after EVERY TIME it goes into the salty stuff. The consequences don't bear thinking about, unless you enjoy working with seized nuts and bolts, and relish the thought of drilling out sheared bolts and screws.

(not my cup of tea)
I'm a mechanic by trade, and i absolutely hate trying to drill out old and crusty nuts and bolts, let alone trying to re-thread a stripped or cross-threaded whatever. Trust me when i say it's mind numbing
A little bit of tlc goes a very long way with these seagulls. They perform well once they've had a close inspection and any corrective work carried out.
Sleeves up and get stuck in.
Jon