You should've replaced the o-rings, but if you didn't it's not a big deal as long as they don't leak. The o-rings would cause an external leak which would be visible. The copper rings would cause an internal leak which could cause problems, but I don't think knocking is one of them. Basically the affected cylinder would have delayed and reduced fuel delivery, causing smoking, rough idle, but not knocking. In fact that cylinder should be quieter as a result. The easiest thing to do at this point is to try that Diesel Purge.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL