FWIW.
I believe you really only need a flexible cable end bush (OEM rubber, spherical or poly) on the lower cable at the transmission end that is related to the forward and backwards movement of the gear stick.
Because the selector shaft geometry is a compromise, that cable flexes sideways at the transmission end, and is the one that tends to break, so a flexible bush helps. It is also claimed that a flexible bush like OEM or poly (but not spherical) will put less shock on your syncros.
The upper cable (related to the side to side movement of the gear stick) doesn't flex sideways like the lower cable, so a cheap ($5) sealed skateboard bearing will do fine there and can give a more positive stick feel.
That cable end is also up high so it is well protected from the mud splash.