Applying a novel and universal action spectroscopic technique, called leak-out spectroscopy, this paper revisits the ν3 proton shuttle motion of the symmetric linear molecule He-H+-He. For this, a 4 K cryogenic ion trap apparatus has been combined with a high-resolution quantum cascade laser operating around 1300 cm-1. Seven rovibrational lines of this fundamental three-nucleus-four-electron system are recorded, demonstrating the suitability of the leak-out method for such fundamental hydrogen-helium cations.