The D has had exhaust problems throughout development and testing. It also had problems with achieving rearward flight certification.
It is too heavy and too small. When fitted with a VIP interior and RIPS, it can carry 2 or3 pax only.
The Medium aircraft game has moved on, sadly, Sikorsky never realised it with the D model. The S-76C++ should have wound down production slowly until sales dried up. The D was Steve Finger's idea, was starved of funds during its Jeff Pino era development cycle as all the money went either to keep the stockholder's happy at the quarterly meetings with UTC or to fix the issues with the S-92.