td4 or auto box oil change

Decided to change my auto gearbox oil yesterday , bought the oil from l r 4 ltrs of AFT 402 + drain washer £40. . . run the motor for bout 10 miles, park up for 15mins, jack up rear and front using proper stands, remember these motors are a lot more heavy than yer standard motor,so don't skimp on safety, put spirit level on inside of door frame to get level, drill out pop rivets on under cowling and remove,find the correct drain plug [look at book and make sure its the correct one, undo, and drain into a clean bucket, drain for 15mins,at this stage you can measure how much oil, should be just under 4ltrs ,but this is not really needed, unless like myself your a geek,put new washer on plug and put back, make up a small funnel, piece of hose,and i used the plastic bit from a standard cartridge gun for the other end,use insulation tape to seal it all, , ,pull out rubber plug inside engine compartment below front of battery insert yer funnel thingy, and slowly pour in yer 4ltrs, no need to worry bout level of oil, as 4ltrs is wot it takes,you will notice a great difference tween the color of old and new oil, put bung back, put sump cover back[at this stage you can mod yer cover for easy removal next time, or re pop rivet] start engine, slide through all gears[without moving] check for leaks , test drive, job done. . .

Nice one Ming. Just supposing I wanted to add oil to my gear box wihtout draining the original. How do you know when it's had enough? There must be some type of overflow plug surely. I think I need to add oil as the gear change is getting very abrupt, not smooth like it used to be.
38k miles, no sign of oil leak but I hear with these symptoms it can mean a lack of oil.

Have got a slight confession, i looked all over for the overflow [it is shown in the Haynes manwell ] but i couldn't find it, rather could not be 100% sure, but i will add again it is most important to get the motor straight,hence the geeky use of a spirit level also put it on both door sills and dont think ,are that looks bout it,get it smack on, if anyone knows the true location of the level plug , maybe a thread. . .

Haynes dont make a manwell for the V6 Hippo which is a poor show
I found the filler bung you spoke of, it's a bloody small hole isn't it? I'm guessing the manwell just shows a small photo of the overflow plug, no particular location?
I've got a spirit level so will make maximum use of it after I locate the overflow plug.
Cheers Ming