Superfish External Pump

[pault]

hello all im a newbie at this so bear with me i have 250l tropical tank which runs a external pump superfish 400. it has been working fine for the last six months the other night i heard a "pop" from under the tank where the pump is kept,upon investigation i found water leaking from around the top cover i removed the pump to strip it down and found no obvious problem so i cleaned everything and got it working again with no problems, however a few hours later same thing happened again. tht only thing was when i removed the top cover and seal water poured out well above the rim of the tub where the filters are kept. by the way this is the type that stops and re-starts every 24 hours to purge air from the system. has anybody had similer problems. thankyou