I was having the same problem with two of my four shocks. I coated all the internal 'guts' with the FT Green Slime and then made sure I used the shock tool to push all the parts firmly into the shock body. Once everything was properly seated and coated I haven't had an issue yet.
Hope that helps, good luck.
Old school RC10
Old School Losi JRx Pro
Previous Rides: B44, RC18MT, RDX PHI, FT RC18T, RC8, TC5(2), RC8T :(