Junk Berserker Question

This is about Junk Berserker's first effect, "You can remove from play 1 "Junk" monster in your Graveyard to select 1 face-up monster your opponent controls. It loses ATK equal to the removed monster's ATK." I checked the rulings and it doesn't say how many times I can use it. It doesn't say once per turn, or when it's summoned, so I'm guessing as long as I have a "Junk" monster to banish. Is that right? I just want to make sure before I start using it.

Edit: I forgot one more thing about this. Do the ATK points it gains last forever?

Correct. You can use it as many times as you can pay the cost.

uh it doesnt gain attack it makes the opponent monster lose att

Oh. I misread it. Sorry.

And yes, the ATK loss is permanent as long as the target monster stay face-up on the field.