If I remember correctly the builders manual for my Model IV from 1994 recommended to put linseed oil or tube oil in through the opening on the fuselage end of the struts and then seal the opening with the same two part epoxy used to bond the ribs to the wing spars.

On the linseed oil...or any oil soaked rags...starting a fire through spontaneous combustion (Exothermic reaction). My neighbor is a professional painter. His work van burned up in his driveway and the fire department said it was due to linseed oil on a rag left in a tool belt hanging in the van. I was really surprised he did that. I thought everyone knows not to do that.