[Old406Kid]

You're correct.
You send in the old, they cut off the guides, and mail them back with the replacement section.

 

[Old406Kid]

Most companies spec in their warranties that you need to remove guides from the effected piece prior to shipping in. So they are not liable for losing them.

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I've had the misfortune of sending in several and have never been instructed to do that.
That being said, I'd be more comfortable doing that and keeping them under my own watch.