I just changed the oil in my E450 and ONAN generator. I found 4 zerks on the front end of the E450 to grease. Did I get them all, or are there more than 4?
The Ball Joints MAY have plugs where you could install grease fittings. I did that on our 2002 Axle. That took the number of fittings up from Four to Eight. When adding Four to the Ball Joints, I chose some angled fittings to make it easier to get the grease gun onto them. Also replaced a few of the Four original ones (as shown on Bruce's excellent diagram) with angled.
Our 2012 Axle doesn't have Grease Fittings OR plugs on the Ball Joints. Sealed for Life? Ford meant it!
Man thats a hard one. I always just look at where they used to be ,tie rod ends upper and lower ball joints, drive shaft /u joints. Many parts are permanently lubed and sealed now.