For what it's worth, most Marxists favor some form of democracy. The libertarian wing favors direct democracy while other tendencies favor different forms of representative democracy. Democracy is favored for exactly the reason that unclear power structures are a kind of oppression and that democracies broadly speaking offer decision making power to the people. A big difference between a Marxist and a liberal is in the analysis of the economic base of power which can either support or undermine democratic structures.