Look here also for some good information

http://www.funkopolis.com:8080/~stuart/cobra/

Sounds like your upper gearset may be going, but yours is a lot older than mine. But, that is the general description of more problems on the way! Save some trouble and get it looked at. You said it felt like you hit something, did it sound like a nice smack of gear teeth??
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Organized people are just too lazy to look for things.