rubber bung on gearbox is to fill it up bud do it asap before you damage it!
As for engine/smoke my Mrs did this car had plumes of white smoke and lacked power/top end speed, 7 miles is nothing get under car with something to catch oil undo the bolt on sump drain oil out replace bolt and refill with exact amount for that car someone on here should know how much! Just do not drive it until you do this