The only maintenance that the average owner can do is change the oil. You will need a “Little Red Hand Transfer Pump” from WalMart or your favorite Auto Supply Store. $10 to $12 bucks. The original oil from GEM is 30 weight. Most of us guys replace it with 90 gear lube. You cannot make a mistake, the gear box will work with any quality oil.
Remove the rubber plug in the cover on the gearbox and pump out as much of the old oil as you can and refill it with new. It’s surprizing how little it takes. I think it’s about 12 oz. Fill to the bottom of the hole.
Gem uses 30 weight to get the most range out of the batteries. Most of us use 90 weight cause it makes us feel good and some claim it reduces whine.