Why would it leak onto the PCB? Anyway I've been using it for years without problems. I'm sure there are better methods but it works
You can use Petrol for all I care , it doesn't mean that it is the right thing to use. And it will leak, by leak I don't mean lavish pouring, but the cloth or fiber that that is doused with the liquid is going to touch or slide over the chip, the PCB side, it is going to have a negative effect.
You have been very lucky if nothing has happened to your stuff until now, is all I can say. I'd suggest google a little on PCB making (DIY) mostly and you'll see what is used to cover a copper plate when we draw circuits on them.