ABS plastic is reccommended simply because it can take higher temperatures and is somewhat stronger. Especially anything around the hot end of the extruder itself. Be aware that switching fillament types especially from ABS back to PLA, you can experiance what appears to be a jammed extruder due to the differences in melting temperatures, if not all of the ABS is out of the nozzle bore when you next try to print. If you run into that situation, extrude the PLA at ABS temperatures for a few minutes until any remaining ABS has been expelled, then lower the temperature back to normal PLA printing temperatures. It’s generally not an issue going from PLA to ABS.
PLA gears will work, ABS gears will last alot longer.