As a member of the public who would like to see one preserved (and one whose father served in the RAF) can I just say that had I been in need of rescue I would not have cared less which service provided the helicopter and crew as long as one appeared in time and succeeded in rescuing me.
Now for a somewhat frivolous suggestion - why not save one, paint it bright pink/orange/purple/whatever service non-specific colour you fancy and provide plenty of visual information on the subject for visitors to the museum? Oh, and make up a number to paint on it so it can't be traced back to a particular service.
