My YS .63 was sitting for about 6 years before I put it back into service. I oiled up the cylinder, fresh glow plug, fresh fuel and started it. I too have heard a lot about the diaphragm going back. Mine is still going strong. I have about 20 flights on it since I put it back in service.

Don't send it in if it does not need it. Run it first.

Dru.