Don't waste a minute of your time trying to collect on a warranty. First, if your not the original owner, or properly transferred the warranty when you took ownership, chances are, it's void. That would be assuming that the original shingle warranty was transferable in the first place. Second if you were told that the shingles had a "forty year warranty" then they came with a document that explains that they are essentially using the words "forty year warranty" as a marketing game, and have no intention of paying anything on your claim. First, you would need to file a claim, then convince a manufacturer's rep. that you indeed have a defective product. Fact is, the vast majority of roof leaks have absolutely nothing to do with product failures, but are installation defects, or failures of related components, flashing, flanges, ridge vents, defective or non-existent ventilation ,etc.... Then if you succeed in proving that the material is defective, once you are past the first five, ten, fifteen years, depending on contract language, you will be receiving a pro-rated credit toward the purchase of new shingles from the manufacturer, that's all. So, the company might end up selling you shingles at a 40-50% discount. You still need to pay for permits, and a roofer to remove of the old roof and install the new one. So at this point a successful claim might result in a new roof that's 20% cheaper than what your neighbor would spend. Now this is all in theory anyway, since you probably are no longer covered by the warranty, and the rep. has a 99% chance of determining that the product is anything but defective.
gravel in the gutter, BTW, is normal and expected as the roof wears. Good luck.