We've had lots of Sprites with flasher problems. For example, indicator lights often stop working, or the whole system becomes intermittent. Our best fix has been to switch to an electronic solid state flasher unit, which can be found here. These babies seem to solve a lot of ills, and work much more reliably. So this is a recommended and inexpensive upgrade, although you may have trouble getting them to work on positive ground system.
If you are keeping your car positive ground, or if you are looking for a more period correct look, then this conventional flasher is what you need. It's always good to have a spare conventional flasher available, so get two!