Had exactly the same problem - and yes, blowing down the tube will work, but doesn't look good.....With mine it wasn't the air seal at all, but the return spring - the coiled spring that pushes the button back out again to its rest place (and charges the air tube with air again, ready for the next push). Yours may not have the same mechanism - but with mine, after much fiddling, stretching the spring out to make it more resistant to the push seemed to work.
Kate Davies
December 2007