Mariner 15 - lowering from full up position

[wneva]

Hello everybody - I have a Mariner 15 from 1999 and I have a problem with the tilt mechanism. The outboard will tilt up nicely, and stays up. The tilt lock seems to work. The problem is I can't then get the engine to lower to the normal drive position. I've tried raising it again to fully up, as the handbook (and common sense) says, and then letting it slowly down. Trouble is, it won't go down. So I have to hold it up with one hand - usually my left - and reach round and down into the water with my right hand to push the lever back against the spring, so the mechanism will operate. In this way I can successfully lower the engine. What worries me is that if I were to lose my grip with my left hand, the engine would fall and damage my right hand. I took it in to my local boat yard where it's been serviced, and the man there couldn't help either. He couldn't see why it won't lower from the raised position without you push the lever back. Has anyone any ideas? Is this a problem anyone else has found?