I spoke to a contact in the FCO in London yesterday, and they are talking to the Embassy in Juba. I think the message has got through, because in a recent and subsequent post on Facebook, Maurice talks about leaving quite soon, as an alternative to going to jail if he stays. He is clearly concerned about his aeroplane but all the advice I have from people in Kenya is that it is in "bandit country" where it is in S Sudan,and it is unlikely that anyone would go there to fix it. The best bet is for it to be put on a truck and taken to Kenya, although a few have commented that it has probably already been stripped of anything useful and is possibly not recoverable.
I fear that from here I can do little more to help, and shall leave it to Maurice, his daughter and close friends to manage the next step. My personal advice to Maurice would be to go to Nairobi if he is fit enough, from where he can manage the aircraft recovery to Kenya; and if not, to return to the UK so that his health recovers. Frankly, the aeroplane, even in the unlikely event of being recoverable, should be his his least concern.