well fixed the diff mount today with a very good and cost effective way i found on the gt4 forums.
i'll give you a quick run through
Remove the mount and mark on some paper the outline and where holes in the middle should be, then cut away the old torn rubber bit and give it a good cleaning, then using the drawing that you done line up where the middle metal piece should be in the middle of the outer frame, then tape up one side like so.
then mix some polyurethane resin, pour it in and when it sets you left with this
a polyurethane rear diff mount for £16:)