Galvanic corrosion between steel and brass is not an issue since there is no electrolyte present. Personally I would opt for the steel rod with heat shrink and a vinyl cap on the end. The vinyl is solvent resistant enough and could easily be replaced if necessary.
I would google the heat shrink and find some that is solvent resistant. Really the heat shrink isn't going to be immersed in the solvent and the possibility of it attacking the heat shrink or vinyl caps is very very minimal.
Typically what occurs with galvanic corrosion is one metal is a sacrificial anode. For example on ships that are in saltwater enviornments. The steel hull is what is supposed to be protected, so sacrificial anodes made from zinc are attached to the hull. The zinc, in the presence of an electrolyte (sea water), corrodes and protects the steel. Galvanic corrosion explained HERE