Thanks guys.
Dave Tyler responded with a "process bashing" of my image and it did reveal the feature in the spot I had seen it, and Elias on CN also said he has captured something similar before, so it might be real. Frank Melillo from ALPO Mercury is going to take a look at it too.
Apparently an IR-pass filter helps to reveal surface detail in Mercury, so it might be worth investing in one if it can also be used on Mars in bad seeing.
Alchemy, yes I'll definitely be going for Uranus and Neptune, and would also love to get Pluto but it will be with my widefield setup so it won't be more than a speck
Focusing was tough, but being a crescent phase made it slightly easier when the sharp frames did pop into focus.
Thanks for commenting.