The reason we ask for sales receipts is so that we can prove when the warranty period began. The warranty period normally begins from date of manufacture, but here at Gravel we are able to extend that period by starting it from the date of the sale to the original owner..
No receipt is never a reason for denying a warranty claim.
Oddly enough, we do have a Marlin 336Y being sent in for warranty service right now, with an issue that sounds very similar to what you are describing. Have your friend contact us so we can take care of him as well.
Thanks for your concern.