In the process of nursing my old Mariner through 12 years and 3000 hours I went
through several of these solenoids. The last ones I bought were sold as lawn
tractor starter solenoids at the BORG and they lasted a lot longer than the
"official" mercury unit. It was an exact fit and about half price.
Merc/OMC does not make these things, they are bought "off the shelf" from a
relay maker, put in a logo'ed box, marked up egregiously and sold as an
"outboard" part.
In their defense, it is not cheap to maintain a part logistics stream, stocking
every part in a motor but you don't need to play.
BTW have you ever bought a bolt at a motor dealer? In one of my rebuilding
projects I replaced every fastener I pulled out. I just dropped them on the
counter at an industrial fastener place and saved about $50, getting superior
bolts.
PS, don't forget the internet. I needed some bolts that were unobtanium in the
US in stainless (commie metric stuff) but were off the shelf in Germany. Even
with shipping they were a lot cheaper than Merc "special order" and I got them
faster.