The bellows gradually loose their elasticity and the seal eventually needs replacing.
I Would look at replacing it at the next haul out
In the meantime there are a few things you can do
Clean the carbon face, some debris trapped can cause leaks
. Pull the bellows back (water will pour in) the water
pressure will help get rid of any debris, but a clean with a cloth is worthwhile.
If this does not work
move the SS face backwards a 1/4 inch at a time until the leak stops. Make sure you mark/ measure the position of he face, occasional a leak is simply caused by the SS face slipping forward, but you need a reference point to tell if this has happened. Put a hose clamp or anode to make sure the SS face cannot slip forward in the future.
Make sure therae is not another cause such as a broken engine
mount or very poor engine alignment.