I'm listening to a podcast about the history of language in the British Isles
http://historyofenglishpodcast.com/and realized I could apply some of the principles of comparive linguistics to delve into the Etymology of seater, takey and mogger.
This is what I've discovered: from latin*, Proto-Indo-European*, Welsh*, Irish* and old English* and Anglo Saxon* we have sella, sedlā, suíochán, sedder and scridwægn.
Obviously all of those* are utter wools so we can at this stage discount the modern
seater as not of Scouse origin. Similarly
backie can be discounted because of its dull ubiquity.
My rearch thus leads me to either
takey or
mogger being the true Liverpudlian term, but further research is of course required ...