I referred to Ps 71 in my sermon this week, and as I looked at the "leaned on" word, it seems to have at its root the idea of "hands-on". If you have a staff, you hands-on the staff to support your weight. It works the other direction too, if someone needs support, you hands-on the weak, to hold them up. So far, no surprises.
But then you find that this is the word for what the priests do with the sacrificial animals. Bring the animal, the priest hands-on it, and then it is sacrificed. I want to be appropriately shy of pushing word-study data too far, but it doesn't seem too much to me to say that the priest in the imposition of hands is "leaning" on the animal, which now is to bear the weight of sin and death. The priest's hands do more than establish a simple identification of the animal with the worshiper. There's a leaning and a bearing.