It is a known problem with the glass feeders. I have several and eventhough they look beautiful they are not very practical. One suggestion I have had is to fill them 3/4 to full which seems to alleviate a bit as they do not seem to leak as much eventhough they still do. I eventually gave in and bought the more practical feeders i.e. Perky Pet and it has been amazing what a change that feeder does for the hummers as well as to my own happiness by seeing them drink of this feeder.
I now hang my glass blown feeders as art (by removing the feeder tubes) and have about 3 other regular feeders that really feed the hummers.

Agatha

I asked the same question this spring. I used a glass feeder last summer and it leaked constantly. It was always covered in ants and bees. Not to mention black mold. It was very hard to clean. Forum members suggested the Hummzinger. This design is much more practical and there is no longer a bee or ant problem.

Will the replacement tube at the following link fit?

I've found with blown glass feeders that filling them up to just overflowing, then pushing in the stopper so that it fills up too, helps stop dripping until the feeder is nearly empty.

I also had to pull out the glass tubes and turn them around backward from how I bought the feeders. The tube has a longer and shorter leg on each side of the bend. Putting the shorter end into the feeder makes the end toward the bird more horizontal than vertical, and that made a big difference for some reason.

Also, wide temperature variations (+/- 30 degrees) overnight make them leak very badly.

Found a replacement tube here too, but the size isn't stated:
http://www.thebirdshed.com/accessories.html
I've never been able to find just the rubber tips anywhere.

Here is a link that might be useful: hummingbird feeder replacement parts