The PVC sleeve is a heat shield between the large heat sink and the capacitor. Leave it on if the replacement cap is as large as the original or just glue it around a smaller cap to create an air gap barrier. Better yet, install the cap on the underside of the F2619 PCB away from the heat source. When you're done, set the trimmer so you get exactly 12.5V between point 01 and ground. This RF power supply board feeds the Dolby board, which specifically requires those 12.5V, so it's important.