The Narco 50 gets hot and shuts off, and the avionics guy says it would cost more to fix than it would be worth. Options seem to be about $500 - 700 for another Narco, with no guarantee it will last; or $1,500 - 2,000 for a new mode C transponder, or $2,500 - $3,500 for a mode S. Since mode S will be needed in about 8 years, if I go new I guess mode S makes the most sense. But I am thinking I would like to do this cheap now.