i think in general things like this is not a problem in itself. The problem is ... hard to describe hmm...
As a confirmed spoiler provider you need 2 things: Spoilers from a source, and a name people know you under. If you post spoilers consistently on a Monday/tuesday, even if vague, your name will naturally gain popularity. Officials WILL get wind of this after some time. Even if it is vague. they will. then they start tracking down. What forum? Where? Language? Can we track IP? Can we shoot the website down he is posting spoilers on? Does he post on his own website? Easy to take down. Call host of website send takedown request or something like that. Post on twitter? Shueisha huge influence, they contact twitter and take account down/get information like ip through contact with twitter staff.
Post on 5ch? Good. but, your name changes. no one will know if you talk bullshit or not no one will know if you are the real deal.
even sites the korean monday leaker used arent safe. As u see, people hated him for posting *so* early. They sent him screenshots of contacting police etc.
again, its about Monday and consistency.
Also after they found you out they will get to know your source and take him to jail too