According to my local boiler engineer (I stopped using the Glow Worm staff after they weren't even able to locate faults on their own equipment) this is a common problem with most Glow Worm boilers. The leak typically comes from the black plastic tube located on left side of the boiler. The part cost £15 and will take about 15minutes to change.
On 2007 models, there is also a fault with the back panel, located on the back of the boiler. This resulted in constant leak coming from my boiler and loss of pressure. I got the boiler leaking for 3 years before the problem was finally identified by my local engineer. If this part is faulty, there is about 2 hours work to change the part as the access is difficult, but this should be covered by the guarantee as it is known factory fault.
Eric
January 2011