my mom had another flat tire on her 2000 Grand Marquis. about 3 years ago when i worked at Sears i had 4 new Goodyear Assurance Triple Treads 225/60/16 H-rated put on. i wanted to use the metal bolt in valve stems but they wouldnt fit on the wheels so i had to use the black valve stems. well she has had her 3rd flat in about 4 months due to the stupid valve stems cracking. luckily i got the road hazard coverage so sears fixed it for free again. the tech that i trained when i worked there did the work so it was done properly. he checked all the tires and found 2 of them besides the one that was flat had cracked valve stems so he just replaced them all. so annoying that you cant even trust valve stems anymore.