Regardless the Rancho warranty claim,You have to go through the reseller.
From Rancho website
LIMITED LIFETIME WARRANTY QUALIFYING PRODUCTS:
Rancho® quickLIFT™
Rancho® RS9000XL™ Shock Absorbers
Rancho® RS7000MT™ Monotube Shock Absorbers
Rancho® RS5000™ Shock Absorbers
Rancho® RS5000X™ Shock Absorbers
Rancho® Light Truck Suspension Components
1-YEAR LIMITED WARRANTY
Rancho® RockGear™ products carry a 1-Year Limited Warranty against defects in materials or workmanship (except finish).
90-DAY LIMITED WARRANTY
Rancho® RS9000XL™ extended length and coil-over shock absorbers carry a 90-Day Limited Warranty against defects in materials or workmanship (except finish).
*Tenneco’s obligation under the Limited Lifetime Warranty, 1-Year Limited Warranty and 90-Day Limited Warranty is limited to replacement of the defective or worn-out product (except finish) with the same (or substantially comparable) product in accordance with this warranty. Cost of removal and installation are not included, and any incidental and consequential damages are excluded under this warranty, regardless of when the failure occurs. The warranties have no cash value and are valid only in North America and Canada. The warranties do not apply to products which have been modified, improperly applied or installed on vehicles used for commercial or racing purposes. Further, these warranties are limited to use on privately owned passenger cars or light trucks. The warranties do not apply to extended length shock absorbers or products not specifically listed for applied vehicle. The warranties do not apply to normal wear components, including, but not limited to, suspension bushings, tie rod ends, ball joints or spherical rod ends.
To make a claim under this warranty, return the worn-out or defective product with the dated original receipt to the dealer or retailer from whom it was purchased or to a Tenneco dealer for verification and exchange under this warranty."
Rancho is not the only company using such approach. I had Mevotech rear control arms that only lasted 8k miles, prob a bad batch like in your case. I called Mevotech and they said they didn't warranty the parts directly and that i had to go through the reseller. I bought the arms from Rockauto so i contacted Rockauto and they sent me brand new rear control arms.
Don't know why Amazon was giving the OP crap on a replacement though, perhaps they didn't have one avaialble when the OP initiatated the claim ? they show both parts available as of today.
Somebody else had the exact same issue as the OP with those isolators couple of months ago, and he said he got the struts in Nov 2019, which basically match the OP 10 month timeline as well.
https://www.ramforum.com/threads/rancho-quicklift-problems.166032/
I know it sucks and again i would't blame the guy for wanting to throw them in the garbage. I won't sugar coat it those isolators are probably crap. I believe a bad batch may be at play. I don't get paid by Rancho just in case i just think chit happens. You see if this was Fox or Bistein people will say it was somebody smoking pot who did the assembly, but when it happens to Rancho or RC the collective minds all come together to complaint about how chitty these products are. Perception is everything. Nobody in this forum seems to have an issue with 5100's washer design and if it's not installed correctly either the strut and/or the top mount can get messed up. Eibach doesn't have that issue because Eibach makes it right.
Write an email to Tenneco and link your thread and the other i posted where they can see pictures. I'm sure you and the other dude who had the same issue won't be the only ones having the same problem . Help the community letting them know there is something ****** up wrong about their isolators or anything they sell.
Check the other strut too and make sure the other isolator is not about to crack. You can always buy 5100's or RC or Eiibach etc or work something out with Amazon and try get the 2nd Rancho strut new. i know i'd like to have both of them new to make sure i don't have to go through the process again, or i'll throw them in the trash and start over with something new.
