I've fixed several machines with this problem, and every time it's been a problem with the actual rubber rollers. Unlike the one in the card reader, I've yet to have one turn to goo, thankfully.
The main problem is getting the roller assembly out. I would seriously recomend getting the service manual that's on the MoHPC CD-ROMs. Then :
Take out the battery, take off the bottom cover (6 screws), slide out the printer paper window, take out the 3 screws, washers, and grommets that hold the printer in place. Unplug the printer PCB from the logic PCB and take the whole lot out.
Unplug the 6 single wires from the PCB, noting their positions (2 white -- home position reed swtich, 2 red -- out-of-paper contact, red and black -- motor). It's difficult to unplug the printhead tapewire from the PCB without damaging it -- one trick that helps is to push a couple of old magnetic cards between the tapewire and the socket connects, then pull the wire out. If you're not happy doing that, leave the printhead connected to the PCB.
Undo the 2 screws holding the metal 'tab' clamp that holds the printhead in place. Slide out the printhead (with the PCB still attached if you've not disconnected it). When reassembling, make sure the printhead is properly seated before fitting the clamp, and tighten the screws carefully and evenly. There is a real risk of cracking the ceramic head if you're not careful.
Mark the position of the home switch, take out the screws and take it off. Take out the 3 screws holding the motor in place and remove that. Take off the E-circlip and remove the idler gear.
Take off the E-circlip and the gear on the end of the leadscrew. Turn the leadscrew to move the carriage away from the RHS of the frame, then press on the leadscrew to force out the RH leadscrew bearing. Slide the carriage and leadscrew towards the right, Push the LH leadscrew bearing to the right (into the frame) and remove that too. Then 'unscrew' the leadscrew from the carriage and remove it through the left side of the printer frame.
Remove the 2 E-clips on the carriage rails _inside the frame_. Take out the rails and remove the carriage. Notice how the ridge on the paper feed roller fits into the carriage. The platten strip will probably fall out at this point.
Unhook the tension springs on the sides of the printer that pull the paper feed pressure shaft forwards. You can now push the feed assembly rearwards and unclip it from the slots at the side.
I've found that carefully rubbing the rubber tyres with 1000-grit wet-n-dry paper (used dry) will greatly improve their grip.
When reassembling, put a smear of plastic grease on the leadscrew, and a bit of dry-film (teflon) lubricant on the carriage rails, the idler gear spindle and the gear teeth.