When should they be replaced? Mine are original as far as I know with 233K on them. My engine starts kind of rough, I am going to start be replaceing the glow plugs and take it from there. But fastlane offers rebuilt injectors for $46.86 should I just replace them all? The seconed one back is leaking fuel real bad, so I will have to remove it to fix it, I was thinking about replaceing half of them now and the other half in a few months. Can you do that or do you have to replace them all at once?

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2006 CL500
2009 C300 4matic
1969 280SE
2023 Ram 1500
2007 Tiara 3200