Is it the one that mounts to the side of the coil bracket. If so that is for radio interference. If it is inline to that tach itself that was to protect the tach if a HEI was installed. If you have a HEI yes you should replace it when you can. If it is the one on the coil bracket and you no longer have points and it is now solid state it's really not needed. Filters were used with all factory HEI installations starting in 75. It is available today