So I took off the glass and practiced the shot. Also, I found out that the metal guide along the outside of the right orbit had shifted a few millimeters, narrowing the entrance the right ramp. I gently pushed it back and wedged 3 layers of foam core in there to keep it in place. It already seems to have made a difference.
I also had to adjust the set screw on the left ramp diverter, as mine was only triggering part of the time, causing situations where you would lock a ball, but it would fail to get diverted over to the right eject saucer. Now all seems to be well again. Ended the last game one shot from finishing the slimer ladder, the right ramp of course, but the difficulty felt more balanced overall and I'm hitting that shot with more regularity after the slight adjustment.