1) Remove magnetic drain plug
2) Allow gearbox oil to drain completely. Tip the bike to the right to get it all out.
3) Remove fill plug (plastic) and oil-level plug (Phillips and 10mm head)
4) Clean drain plug and replace
5) Fill with 700mL (700c.c.) of fresh gearbox oil
6) Oil should drip out of oil-level plug with the bike absolutely level (i.e. if bike is on a rear stand, also use a front stand). If oil does not drip out, add more oil and allow all the excess to run out of this hole. DO NOT OVERFILL!
7) Make sure the oil level is even with this hole.
8) Replace oil-level plug and plastic fill plug.
9) Go ride!!!
Notes: We changed our gearbox oil after every race weekend. It uses less than 1 quart and is relatively cheap and easy to change out. Also, allow any excess to drain completely before replacing oil-level plug.