Correct oil for the gearbox is ATF, whatever you do don't use the gear-oil you put in the transfer-box. I am sure someone will be along in the minute with the detailed specification of the ATF (it is listed in the handbook & workshop manual anyway) but any decent fluid should do. I used Comma and replaced it every 12-months as that way it gave a good quality change (far better than the change on my R380 has ever been even from new or when filled with synthetic oil).