Anyone ever been able to reenlist in the Marines with an honorable discharge but an RE-3C ?

Answer 1

You shouldn't have an issue with that. It is a waiver but what is important is the 3 letter code that goes with it describing the issue. It's on you DD214. If it's a medical issue, you'll have to supply the meps doc with enough documentation that the condition is resolved and then, based on his opinion, he will recommend a waiver.