Volva SX-M sterndrive trim line leak

[renohawkfan]

I have a Volva SX-M sterndrive that has had intermittent leaks (4-5 times over several years) of the lower (inner) port line. I have generally just replaced the o-ring that goes between the line fitting and then cylinder and that has seemed to work and holds fine for some time until it doesn't (usually 2-3 years later or more). I just did that again, but it leaked again within a couple of weeks. Working throught the options, it seems to be either the line fitting, the cylinder (or where it screws inside the cylinder), or the o-ring. It could be related to the position it is stored in and torque on that connection. Replacing the line (a $50-80 part) requires you basically take the drive off, which is a job, but can be done. The cylinder is more costly. So far, I believe it is the fitting.

Any suggestions? Had a buddy suggest a slightly fatter o-ring.