Provided are methods for extending the life of in-service electrical cable having polymeric insulation, comprising injecting into the cable a dielectric gel formulation containing: (a) Si—H endblocked polydiorganosiloxane (H(R2SiO)x(R2Si)H); (b) polydiorganosiloxane endblocked with unsaturated carbon-carbon functionality; (c) hydrosilylation catalyst suitable to cure (a) and (b); and (d) at least one organoalkoxysilane functional additive (e.g., anti-oxidant-based alkoxysilane, voltage stabilizer-based alkoxysilane, hindered amine light stabilizer (HALS)-based alkoxylsilane, UV absorber-based alkoxysilane, etc.), wherein (a) and (b) are cured post-injection into a non-flowable gel, and wherein (d) diffuses into the insulation. The methods may further comprise a hydrolysis/condensation catalyst compatible with the hydrosilylation catalyst so as not to interfere with the cure of (a), (b) and (c), and/or be compatible with optional siloxane crosslinkers, and/or with optional hydrosilylation inhibitors.