If I remember correctly, your 220D is a '70 model. Does it not have an all metal banjo bolts and metal tubing return system until the one rubber connection toward the filter? If that is the case, there is only a very small likelyhood that any of that metal system just started leaking. The rubber leaking should not appear to show up as an injector leak, since it is so far away. Could well be the injector to block or PC chamber joint.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150