disco 1 door mirror glass

[120a]

hi all have abeen asked by a friend to fir a new mirror glass to his discovery 1, looked at the mirror today before ordering anything and is there meant to be a plate in there the same as a disco 2. looking at the current mirror you have a rectangular shaped piece of plastic with two slots in each end. i presume the new mirror glass just slots into this. just thought id check as i know td5 and so on mirros have a plastic adaptor that goes in between the glass and mirror.
any help appreciated