The cheaper ones usually have a rubber plug where they were filled..
Sometimes those plugs will pop off or leak..
The ones I prefer, have a brass plug that screws into the housing rather than the rubber plug.. but they cost more..
Before I knew this... I used to sell the ones with the rubber plugs and after having to replace a few.. I stopped selling them.

Build it the way you want it ..... then learn how to ride it like you own it..
www.lowridersbysummers.com