2001 diesel Santa Fe flywheel

While I'm not an expert on modern cars, I can't imagine why you'd need to replace the flywheel, unless you are simply wanting to replace it with a lighter weight flywheel for better performance.

In old cars, the flywheel serves several purposes:
1) provide inertia to keep the engine idling smoothly (keep the crankshaft spinning more evenly)
2) a large gear (the ring gear pressed onto the flywheel) to give a low-torque way of turning the engine (for the starter to start the engine)
3) a surface for the clutch pressure plate to mate with and for the clutch cover to bolt to.

Unless the flywheel or ring gear is severely damaged, I see no reason why you'd need to replace it.

I'm not sure what a "dual mass" flywheel is, but in any case, I'm pretty sure it serves the same purposes I described above in a modern car as well.

Kelly