I personally never trust anything that says lifetime guarantee. It just can't happen except in very unusual circumstances.

I do have an anecdote that disproves my theory, however. My grandmother used to be an AT&T telephone operator, before they were broken up. As a retiree, she has "free lifetime AT&T", which they have been honoring even as the new company is not the company she retired from. She literally dials 0 and asks the person to connect her call for her. It costs her nothing.