well... I have no idea what kind of warranty policy Sears or Amazon has, but:
As a buyer for a retail chain of auto parts stores, I wrote purchase orders for Kastar Tool for over 15 years. Good product line - feeler gauges, mostly... some other oddball "fix it" items like your "thread restorer kit".
I had absolutely NO problem either with the factory or with the manufacturers' agents who represented the line on "warranty" issues; they just wrote it up and issued us a credit.
When I got out of that business I went into outside sales and worked as an independent manufacturers' agent, and Kastar was one of the lines we represented. Good line. I believe it was a 4% or 5% commission line - which is real gravy. Wrote up a $3600 purchase order one afternoon at the "Tool Town" store up in Des Moines. (Smoky, who was the owner of the "Tool Town" chain, blew a gasket, but it was his little brother who wrote the order, so what could he do?)
Never hassled any accounts on "warranty" returns - just wrote it up and issued a credit. GAW (General Automotive Warehouse, who owned Al's Auto Supply) was probably our biggest account. The amount of "warranty" returns on Kastar was really piddly compared to some other lines like Harada Antenna or Cobra Wire & Cable. I just wrote it up - no hassle.
I suppose you could always contact the factory and see what their current policy is, but when I was selling it we didn't hassle the customer on "warranty".
Good line. Kastar is OE on tons of stuff peddled under various names - all those laminated double-end ratcheting box wrenches are made by Kastar - every one of them. They also make most of the feeler gauges sold by most other companies, as well as those "thread fixer" deals and the snap-ring pliers.
Just my two cents. YMMV.
