Saving Old Seagulls

Hi, probably simple answer but much appreciated as new to the world of seagulls!
Have a 1960 century that doesn’t go into gear. I removed the three screws to remove the cover at the back of the prop. Just had dirty water and sludge in it.
The bevel pinion seems to just drops down out of the square drive shaft when the moter is upright so that it doesn’t make contact with the gear teeth on the crown gear and hence no drive.
My question is should the bevel pinion be fixed into the square drive shaft to hold it in place or is something else wrong. The square drive shaft is corroded at the end but still fairly square. The gears themselves look ok but lots of play in the propeller shaft and the unit is clearly not holding gear oil.
Your expert thoughts appreciated as otherwise the motor runs sweet. Is it repairable or should I be looking to pass on for spares.

Photos & the motor serial number would give a clear picture of which gearbox your asking the question about.

Welcome to the forum

I don’t quite understand what you mean. Can you post pictures? The bevel gear cannot drop, as the crown gear sits below it.

I would fill your gearbox with WD40, or paraffin. Leave it a couple of days, drain and repeat, to get all the crud out. Then you will be able to see what is going on. It does sound like your lower unit has had a hard time.

The clutch mechanism is simple. The shaft moves in and out, and engages a dog on the crowngear to rotate the prop shaft when you lift the clutch lever.

"I removed the three screws to remove the cover at the back of the prop", could make that an FNR box.

Century plus has 3 flange screws

At the back of the prop?

He means the end cover.