Find out what case, on the bottom left side is the case number. What are the last 3 numbers 741.742,or 489. There are pluses and minuses to each one. 741 is under rated because of a supposed weaker pinion shaft. Not true, but the available new gear ratio’s is very limited. 742 is good because the pinion preload is set through shims. As is the 741. No crush sleeve that can lose preload and once you have the needed shim thickness you can remove the pinion to replace the seal and just tighten the pinion nut. 742 has a good number of new gear sets available. 489 is good, but uses a crush sleeve. You can get a kit for it that converts it to shims fir preload. The different pinions don’t matter in regards to strength. 8 3/4” don’t really break the pinion. They hammer the carrier bearing caps and knock the adjusters out.