I have a document feeder (DF 318) that is jamming. It is getting caught up on the paper guide right after the slit glass. The guide guide is broken up into 5 sections with pinch rollers in between them. It appears that it hangs up on the 2nd to rear guide. The slit glass and the white roller right above the slit glass seems fine and so doesn't the guide it is hanging up on. I just don't feel replacing that guide will fix anthing.
Those guide sections do wear and crack, it may also be the rear holder for the white transport roller is broken! The black plastic bits that allow that roller to move a bit, the roller is held in place by the small springs. Also check the height of the feeder is correct.