Sealed? In a sense, yes, but having no o-rings, or gasket, the gear diff won't hold fluid for any good length of time.The diff is sealed. Most diffs are all sealed.
Here's a link to traxxas and all there older RC. If you want to down load the spec for the truck. Down load hawk or hawk2.
https://traxxas.com/support/PDF-Downloads-Legacy-Models
89 or 92. Either one should work and help with the break down and rebuild. And for any part numbers that you need bud