Yea, $300 would be worth doing! If you could learn how to balance the tensions, check and set all the timing settings, open the machine and clean and oil throughout, service the motor, check for burrs and polish them out, etc. If you get those things down, you can figure out the rest. The hardest part about working with machines like your Janome, is getting the dang thing open without damaging the connections to the circuit board. LOL! But you can usually do most work on that machine without opening the machine up.