My grandson drove the atv without any gear oil in the gear box,the wheels locked,and it would not click n gear,I then filled the gear box with gear oil, it unlocked ,but it shifts a tiny bit hard here and there ,but now i have a gear oil leak on the left side of the motor, right at the bottom corner screw of the crankcase cover, what is the problem and is it a bit fix

 

This is a how long is a piece of string question, as we don't know the make. Most quads have the engine and gear oil shared, so it isn't a common make. At a guess I would think the gasket has gone so, case off, fit new gasket, or it may just be sealed with "goo," but expect a shower of gears and washers to drop out when you take the case off.