Yes, I'm familiar with this (on Sea Rays). Grady (like Sea Ray) doesn't have anything to do with the number of duckbills used - Dometic/Sealand is the manufacturer and they designed the system. Grady/Sea Ray simply plopped it in there. All Vacuflush systems use (4) duckbills (2 in, 2 out) at the vac pump. Replacement is about as easy as it gets - very straight forward. Access to it... that all depends on the boat. On some it's super easy, others not so much - THAT part, though, you can blame on Grady/Sea Ray/whomever!
But then... manufacturers have it tough - trying to find room for a lot of systems in a small amount of space. The only thing you'd need to verify is whether or not your system uses 1-1/2" duckbills (basically, hose size) or 2". If I had to guess, I'd say 1-1/2" based on a relatively short run of the hoses from toilet to tank - but double check.
If the system is currently building vacuum quickly and the pump doesn't run on it's own (losing vacuum) every so often, I wouldn't worry about. They typically don't "just go bad" all of a sudden. Performance slowly drops.
FYI, where you might be getting confused on the number of duckbills used... Most Sea Rays use a similar type of pump system (to the Vac system) as a macerator - however the mac pump uses (2) duckbills (one in, one out).
Do a bunch of flushes with some water and treatment chemical first!