Add to the list check the front axle pivot point for play. There should be no movement of the diff case front to back. It should not pivot side to side. (one wheel forward the other backward). If the pivot pin is worn badly it can break and the front axle will fold under the tractor. I had this happen once and it is scary. lucky for me I was running in low cog at the time. Check all tie rod ends. Check final drive front hubs. When you turn the steering whele you shod not have more then 1/4 turn of play before you see a front wheel begin to turn. Wobble can be cause by a bent wheel very bad tire , loose linkage, or bad pivot point, hub bearings , or bent hub.