If you aren't in the habit of keeping receipts for tax deduction purposes, you lose the chance to do it. (exclusive-executive-resumes.com)
It is always recommended that you submit proof of purchase, but it is not necessarily required because people do not usually keep the receipts of all their purchases with them. (travelinsurancereview.net)
Just keep the receipts in case you ever need to prove that the maintenance was done. (articles.orlandosentinel.com)