Well, since it was such a simple fix and the mower is so powerful, I decided to keep it. I may put a cover to protect the innards this time, but meanwhile, the spring I put is not the exact one and it seems to be running the engine too quickly. Lars did you ever get ahold of the original spring or find a suitable replacement? I'll post back if I find one, as well.
Thanks for your post! Unfortunately if this happens so easily I'll definitely be returning this mower. That explains why it was so sudden. And as I look at the engine at the cheap plastic parts I can't believe there isn't a cover or something...the pieces will get broken very easily it looks like.