Geoff, I'm serious this time. If you're going to replace one coil, you MUST replace the other if it's a 2 coil door. They're also not easy to install by yourself. About 4 weeks ago, one of my coils snapped and I swear this would have decapitated anyone in the garage at the time based on the damage it did. I hurried out and bought a coil and started the installation process. Well, this is/was a 20 year old door and hardware and as I tried to install the new coil, I noticed that the cables and everything else was very weak. I had the garage door dudes over to look at it and they are replacing everything this coming Wednesday. The door itself still looks like new but....I'd rather replace it than play around with the mechanics of it.
edit: HA! Sorry Art...you were way ahead of me.