lost drive on flymo qs5160hw?

iv got a flymo qs5160hw.
iv aquired it with the self propelled drive not working, we'v ordered a new spring from flymo (retaining spring)
& been told to attach one end to the gearbox casing & the other to the body.
we'v tried this however its pulling the gearbox the wrong way & not tensioning the belt!
iv contacted flymo for a illustartion of the parts thats meant to be there incase theres a piece missing however theyv replied saying that they will not give out such info as repairs should be carried out by a dealer! hehehaha!
is there a piece missing?
i have searched the net looking for a diagram/manual etc but found nothing.
there was a similar post on here with the same problem but the answer was the same as the dealer & it doesnt work. any info diagram would be greatly apreciated as im a bit lost!

i am assuming that there is many mowers with the same type of running gear eg same set up belt needs tensioning to the gearbox.
thank you in advance