The lifters in my wife's 97 Trooper are making noise at 135k miles. I have changed the oil every 3k miles consistantly but the noisey lifters come and go. The dealership wants close to $2000 (cost of parts only) to replace all of them and I guess there are 24, and other automotive places can't get them. Where can I buy replacements at a reasonable price and or would it be better to just spend that 2k towards the cost of a replacement remanufactured engine?