MichaelRLopez/iStock Editorial via Getty Images While shares of Marathon Petroleum (NYSE:MPC) are up substantially over the past year, they have been a poor performer over the past few months, dropping about 25% from their 52-week high, as concerns have built over the health of the refining cycle. I last covered MPC in March, downgrading shares from a “strong buy” to a “buy.” While shares did briefly rally to my $216 target, in hindsight, I did not downgrade shares strongly enough as they have fallen by ...