Returning the the airworthiness aspects of the situation, I can find no EASA emergency airworthiness directive having the effect of grounding the Hoffmann propellers fitted to the G115E. Therefore, EASA has yet to determine that an unsafe condition exists. This continues to suggest to me that the issue is one of MOD duty of care and that the contractor will not be liable for the costs.
How's your German?
http://www2.lba.de/dokumente/lta/2004-352R2.pdf