Mercedes 126 722 auto transmission fully rebuilt 5K miles ago; now AT oil is disappearing at a rate of 1 quart per month; absolutely no leaks visible anywhere under the car; dry as a bone; no leaks visible from dipstick, new oil cooler lines dry as a bone; no leaks at front seal; no leaks at rear main seal; where is the oil going? what is the cause? what is the fix?