if the "small allen" screws have loosened up ... you should have 2, one on top of the other, so remove both and see, it may be a simple as piece of crud as mentioned previously ... but had mine loosened up ... scared the bejus out of me ...

... realized what it was immediately (we had just lowered sails and was about to enter the cut in Roche Hbr / Garrison Bay ... and I noticed the auto bilge pump working overtime) although the admiral was wondering why I was pulling everything out of the port locker in a mad hatter type of rush to get to my shaft and pss ...

.. a quick check is - see if you can move it along the shaft easily ...

... I could, snugged it up and then located my mini allen wrench and cleaned and re-tightened it all ...

... that was after ~10 years ... I generally burp it every week but it seems to be doing better than it used to (created a vibration when it was dry) as it doesn't seem to ever vibrate anymore?

... perhaps its self polishing or??

... when and if I ever change out my shaft or need to pull the transmission I would replace it with the vented one but like they say

"if it ain't broke don't fix it"

... so many toys and never enough time to play with them ... general maintenance and the usual upgrades is enough of a time monger ... I'm not looking for more projects and personally I'd rather use my toys than be constantly working on them ... (boats, motorcycles, bicycles, ski's, etc ...not to mention the necessary evil ... auto's...)

Ain't life grand!