You probably know the Mariner was a short lived marriage between Mercury and Yamaha. Nothing wrong with that and Yamaha bought out the Mariner brand when they split up. Just a heads up that some parts were Mercury and some Yamaha so once you figure out which is which you have two sources for parts. I bought a 55 HP 2 cylinder Yamaha and was puzzled as to why all the 40s and 50s were 3 cylinder and this had 2. Turns out it was a left over Mariner that was re-branded and sold under the Yamaha cover.
Never had a parts issue because it ran like a scalded dog and never gave me a minute's trouble. In retrospect I wish I had kept that boat.