Makerbot 5th generation leveling problem

[mlinke]

I always find that my back left corner is a bit too low, and the raft on that side will curl. Usually this causes the bottom surface of my parts to be curved slightly at that corner. I can observe on the raft that's printed that the front right corner prints very straight lines, while the furth back and to the left i look, the initial raft layer beads as the filament is extruded from progressively higher z-distance.

I believe i can manually account for this by adjust the leveling nobs, but i'm wondering if there are any known causes for this or settings i can adjust on the printer.

For reference, the levelling process checks a "first position" and "second position". Considering the "first position" to be the "front" and the second position to be the "right", it's the opposite corner, the back-left, that tends to be too low.

Is this a "z-axis offset" thing I've been reading about?

Moderator note: First post approved! Welcome to 3DPrintBoard.