This is only happening with duplexed prints; standard prints are coming out flawless. I have replaced the duplexer unit, which has not fixed the issue. I am only using genuine Konica Minolta High-Yield toner -- it's dirt cheap nowadays -- and have also replaced the drum unit -- again genuine. I have cleaned the various rollers that are accessible from inside the top cover. I did recently adjust the Registration Roller Solenoid, but did not replace the worn felt pad. Could this be causing the issue?

Office Equipment & Supplies - Xerox