Alright so I been wondering about this for awhile my forward driveshaft is rusty and my rear one looks brand new. replace or is it fine? I tapped on it with a wrench and it sounded solid

 

check the u-joints, the shaft doesn't matter

 

You could sand, prime and paint it, but it wont cause any issues with rust on it.

 

Just make sure to hit the zerk fittings on it for the u joints and slip yoke. If you're worried about it you could always remove the driveshaft and make sure all the joints are good, but i wouldn't worry too much about some surface rust.