Ok, I've had these Plaz pads for over a year now I think, and they've barely worn. They've been on several grinds, some of which have been quite harsh. And 3 rims. They just don't lock. I've got some Zoo pads at the moment, and they're wearing fast on my worn out grind, and at a funny angle. So I wanna use these Plaz again. I've tried de-greasing them before, and filing them down a bit to get dirt off, but still no luck? Is there anything else I can try to get them back to locking like they used to? I don't really want to have to use tar all the time, or keep grinding my rim. They used to work super good, even on a worn grind!