I replaced the copper o-rings on my 1985 300D within the past week. Once I removed the part that the "spider" screws (this is called the "pipe connection" ) onto at the injection pump and pull the spring out I took a magnet and pulled the part out that the spring holds down (this is called the "delivery valve" and the part underneath it came out too (this is called the "delivery valve holder". Look underneath the "delivery valve holder" and you should see the copper gasket. The MB part number for the copper gasket on my 300D was 000-074-17-59 and is called "gasket, injector" on the bag label. It goes on to say slightly lubricate the threads of the pipe connection and tighten ot 40-50 Nm in ONE STEP. I used Marvel Mystery Oil to lube the threads because that is what is in my squirt can
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