Synthetic oil recommendations

so my aunt picked up a new cub LTX 1046 with the kawasaki eighteen five hp
they say to change it after 12 hours so I have decided its gonna get nothing but Synthetic the problem is what brand I run nothing but rotella or Mobile 1 in my stuff but I hear that the kawa's have plastic gears so anyone know if the syth oil will eat the gears/cam ?
also anyone have any details on these motors iv never had a machine with a kawasaki motor but since kohler has gone down the crapper didn't really have much of a choice