I have used one of these to sneak past the boot seal and grease up w/ grease gun,need to be carefull about not piercing the boot.You can do this if the seal (tapered end) is wearing and grease is starting to come out,It will buy lots of time atlease before replacing
.But No, once the boot rips or once the joint has play,need to replace...Actually I do not remember any Toyota ever having ball joints upper or lower having greese fittings,..Just on drive shaft.
Plews 05-037 - Grease Gun Adapter Injector Needle 18Ga x 1-1/2in.
I think I found it at autozone by the grease guns.
here is what it looks like: