If the de-soldering pump o-ring is made of silicone, the use of silicone oil is appropriate. Petroleum based oil will deteriorate rubber similar to using condoms with oil based lube.
"NONCORROSIVE FLUXES.— Noncorrosive fluxes are
for soldering electrical connections and for other work that must be free of any trace of corrosive residue. Rosin is the most commonly used noncorrosive flux. In the solid state, rosin is inactive and noncorrosive. When heated, it melts and provides some fluxing action. Rosin is available in powder, paste, or liquid form. Rosin fluxes frequently leave a brown residue. This residue is nonconductive and sometimes difficult to remove. The removal problem can be reduced by adding a small amount of turpentine to the rosin. Glycerine is added to the rosin to make the flux more effective.
CORROSIVE FLUXES.— Corrosive fluxes have the most effective cleaning action, but any trace of corrosive flux that remains on the work can cause corrosion later. For this reason,
corrosive fluxes are not used on electrical connections or other work where corrosion would cause a serious problem.
The most commonly used corrosive fluxes are salammoniac (ammonium chloride) and zinc chloride. These fluxes are frequently used in either solution or in paste form. The solvent, if present, evaporates as the work heats, leaving a layer of solid flux on the work. When the metal reaches the soldering temperature, this layer of flux melts, partially decomposes, and liberates hydrochloric acid. The hydrochloric acid dissolves the oxides from the work surfaces and the solder, making them ready for soldering." -
Source