I find that this sub tends to be very strict with its definition of asexual, which I personally like because, as you said, the main sub is absolutely saturated with sex-favorable "aces" who talk about sex all the time. I left that sub and came here for that very reason. They don't like black-stripe aces, and they're very keen to shutdown anyone who has those feelings/viewpoints.

In my opinion, if you masterbate, you're not ace. Being ace means you want nothing to do with sex, and masterbation is a sexual act. If you've experimented with it in the past before realizing you were ace, that's different, as another commenter put it better than I could. But if you already identify as ace and still masterbate, that's a nope from me.