OK, I mis-read your post at first. The owner's manual does say fold it in or risk damaging the hinge.  Just for everyone's reading pleasure here is an excerpt from the owner's manual of a J & M 525 cart. http://www.jm-inc.com/new/maintenance/Cart-525-620.pdf

LOADING AND UNLOADING THE GRAIN CART
1) With the gate indicator in the closed position, fill the tank with grain.
2) With the PTO disengaged, fold discharge auger to upright position.
3) IMPORTANT: After the auger is in the upright position, be sure to start the PTO at a SLOW RATE OF SPEED until the lugs on the upper auger engage the drive dog on the bottom auger (failure to follow this procedure may cause extensive damage to both the drive dog and drive line.)
4) Increase PTO speed and open the inner gate until the pointer is in the half-way position. When grain begins flowing from the discharge auger, open gate to the full position.
5) Once the grain has ceased to flow, return the gate to the closed position (for complete cleanout, gradually close gate, allowing the opening to be reduced). Disengage the PTO and allow its rotation to come to a complete stop. Auger is now ready to be returned to the stow position. (Important - Do Not Pull the grain cart through the field with the unloading auger in the upright position. Failure to return the auger to the lowered position may damage hinge and greatly reduce the life of the auger system.)  [emphasis mine]

In plain terms: Treat it like your private parts and put it away when you're not using it.