I keep meaning to go through my box of spares for you and see what I have, seeing this post has reminded me tbh, sorry!
Although if I haven't, if you remove the whole thing you could get creative with a cut up yoghurt pot and some epoxy to fill the hole, or fibreglass?
Or plan C is probably to find the cheapest, most rattiest matching model on ebay and use it for spares. If the physical shape of the machine is the same the back end will fit. Even the fancy push button adjustment ones are the same, all the 'logic' is in that part, it just plugs into the motor and cord reel loom and does it's thing.
I'll have a look over the weekend for you and report back! I've got a few back end parts, but not fully sure I have one of those...