tcase should have nothing to do with your shifting problems - if your 4lo works and you get no add nooises when turning i would check the tcase fluid , make sure its topped off, and forget about it -the borg warner tcases we have are supposed to be extremely reliable i have no idea what happened to mine - i think im just unlucky - as far as changing the fluid we use transmission fluid in the tcase not gear oil - and the fill plug should be above the drain plug somewhere i dont have the vx at my house or i would check for sure but i remember it was not difficult at all to add/change fluid - basically take out both plugs, drain, replace bottom plug, fill till it pours out of top plug, and replace top plug - im pretty sure you do not have to have the vehicle running like when you add trans fluid