The ferrules on many old rods had no water seals in them. The water seals in some of the better rods were just press-fit. How well will that seal? If it bothers you you can put a coat of epoxy on the end of the bamboo before you install the ferrule. There are some very well known rod makers making some very expensive rods today without water seals in the ferrules.
Here is some food for thought, a bamboo rod with bamboo ferrules is acceptable to a large number of bamboo rod buying folks. The bamboo is open to the elements. A ferrule with no water check is not acceptable to the same people. Double standard? Inflated expectations?
The decision is yours to do what ever you are comfortable with.
Enjoy your project,