The dealers are forever telling us to run their 'genuine' brand oils but we choose to use 3rd party oils. To make sure we didn't compromise our warranties we asked our supplier for their specs and product breakdown. We asked the tractor dealer too but they didn't want to comply so we had their oil tested ourselves. The 3rd party oil was superior in some areas (VI and TBN), similar in others (zinc and phosphorous) but about 15% lower in calcium and had no magnesium (OEM had 120 ppm). Our supplier said that as these were primarily diesel engine detergent/dispersant additives they were not so important in a tractor transmission. Can anyone suggest why the OEM oil would have det/dis levels similar to our diesel engine oil?