Yanmar sail drive troubleshooting advice needed.

[Privilege]

I've got a SD31 sail drive which won't go into gear. This started half an hour after I'd given it an oil change, putting in the correct amount of manufacturer recommended 80/90w and not overfilling it.
I've taken the top gearbox assembly apart and everything seems fine. I cleaned the dog clutch anyway and reassembled it. Before putting the top cover back on, I held down the top of the gear shaft and the clutch was popping up and down nicely in response to the gear lever but when everything was reassembled the problem remains
When I had the clutch disassembled, I put it back onto the sleeve at the top of the leg drive and turned it by hand. It did turn the prop albeit with a funny clicking noise. When I reassembled everything the gear shift lever sounded like it was still working fine with the forward and reverse gears both clicking properly as the clutch pops up or down. When the lever is engaged the drive makes a rattling noise as if teeth are not engaging and the prop won't turn.
It sounds as if something has gone wrong in the lower leg but I thought I'd seek advice from the forum before I have to slip the boat.
Any thoughts?
Thanks.

[Tellie]

How old are the props? I worked on a boat a few years ago that had a prop issue on ther sail drive with the binding material that makes the mechanical connection between the spline and the prop itself. We thought we had a bad leg because it felt that it wouldn't go into gear when actually the spline was spinning within the prop. Funny thing was that it did not happen all the time. A long shot but might be worth taking a look.

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[Privilege]

Tellie, thanks for your input. What a good idea, I hadn't considered that. It could have saved me $1k but instead all it did was get me wet and cold!

However, while down at my props, I think that I may have found the problem. The lower gear housing bolts have loosened up where the zincs have corroded and the housing has come out of the leg by about an 1/8". It's not enough to allow water in past the oil seals but may be enough to disengage one or more of the gears. It's on the list of things to fix. Thanks again.