AppleArcade The Oregon Trail: What does wagon grease do?

In the AppleArcade version of the Oregon Trail, the purpose of wagon grease is described as increasing the wagon’s resistance to damage. When used, the wagon glows green for a moment with some + symbols hovering around it. However, from my experience it does not really seem to do anything, and I can’t find a menu showing the wagon’s current damage resistance or anything like that. So does it actually work, or could it be bugged? It’s very inexpensive so perhaps it works but doesn’t have much effect?