There are no seals of any sort, just tolerance between the shaft/tube and the viscosity of the grease. If the tube is full it works very well at keeping water out. When I start sliding the shaft back down I keep a firm finger over that bottom hole to keep any grease from coming out there, any excess can squeeze out the top. This keeps the tube full with no air gaps in the lube, effectively pressure lubing. Always used the HT Blu Lube with great results.