gday everyone. i have an 08 gsxr 750 and pulled my front wheel off a week ago to have the tyre changed. while it was off my son squeezed the brake lever. now with the wheel back on the brakes feel like they need to be bled. they pump up ok and lock the front wheel fine but as soon as you move the bike more than a metre or so the lever goes to the bar then needs to be pumped up again. i bled it once, same problem. tied the lever to the handlebar for 12 or so hours hoping if its got a bubble to move it but still same problem. anyone heard of pistons sinking back into the caliper or something like that? any ideas to remedy it? cheers for any help.