The RAC doesn’t have a date of expiration. As long as its polarity doesn’t change, it works for ever. The polarity can change if it falls down or hit hard by something, or by loud sounds like jack hammer or disco music etc. If we know before hand that such a sound is going to happen, the way to protect the RAC is, while the sound endures, to place it in an horizontal position in the direction of East West. In this position RAC doesn’t work. When the RAC is not in function, its polarity is not affected by loud sounds.
However, in the case that it receives a blow or an unexpected exposure to loud sound, in order to make it again functional, either you send it to someone trained to fix it or if you think that you could learn to use the pendulum, ask for instructions to do it yourself.