Just thought I'd best check... I'm re-filling my gearbox and final drive oil through the dipstick hole. Is that the right thing to do? (1989 3.0 12V V6) I'm sure I've done it that way before in the past, but my mind's a blank right now! The workshop manual isn't especially illuminating. It just says "...and re-fill". There isn't a separate filler hole for the gearbox and for the diff, is there?