10 year guarantee

Euroseal offer a 10 year insurance backed guarantee of the work, but it
appears this does not apply to repairs they carry out under that
guarantee.
I had a faulty patio door handle replaced towards the end of the
warranty period. Within weeks the door would not lock at all. When I
contacted Euroseal their manager told me that the repair was only under
warranty until the end of the guarantee period which had by now expired.
Do they not expect their repairs to last? I do not expect a 10 year
guarantee, but would expect the replacement handle to be warrantied for
12 months - not 8 weeks.
What does this say about the standard of repair offered by the 10 year
guarantee?? Euroseal were slow to repair a faulty door handle on my patio doors under their 10 year guarantee. When they did repair it the handle failed within 2 months. When I contacted them they said the 10 year warranty had now expired so they were not liable. It appears that they had done a poor repair job and they then don't guarantee the repairs at all. I do not expect a 10 year guarantee on repairs, but I expect them to last for 12 months.