I have the official logitech wheel, and I too suffered and continue to suffer from the brake slightly being pressed problem after a replacement pedal.
It is all down to GT5's lack of deadzone settings. The few cars I drove seems to have it. Yeah, logitech could have introduced the deadzone in hardware level, but this is against customization by all means. And being the official wheel, it has its problems of sending false input, but the problem is there, and it is totally ruining the game for me. The problem vanishes for a few minutes if I disconnect-reconnect the wheel's usb, but I have to pause. It is not only ruins all the immersion, it is something completely impossible on a multiplayer game.
Btw, as you can guess from the first paragraph, I had returned the wheel for this problem, and logitech replaced it with another model's pedal (some momo version pedal), but the problem arose after a few hours of play. So that's two pedals with the same problems.
GT5 should have a deadzone setting, period. It is heck not hard to implement. And this problem is ruining the game for the official wheel, and PD should do. Where do I sign a petition?
Frankly, I find it absurd they are modeling even text details inside the cars headlights, but they don't bring customization options for deadzones and have them straight at 0%(which should be there even if this problem wasn't there). Kazunori the perfectionist may want perfect hardware, but there's no such thing.