S11·E42 Doc Brock!

Brock is away on an errand. When they can't handle it, they send Gliscor to bring Brock back. Brock finds he can't carry Gliscor back, as it can't glide in the wind going the opposite direction, and leaves it, promising to return for it. At the end of the episode, the gang comically realizes that they left Gliscor behind, and scene shows a frustrated Gliscor with a long way to go.