Yes, a picture would really be handy here. David's explanation pretty much covers it but let me add MB's parts descriptions to the order.
First you remove the injection lines. They were screwed to the "pressure valve holder". This is what needs to be retorqued and yes, the reason is that the leaks may be solved with just a retorque. There are two types of leaks here. One is external (makes a mess) and one is internal (causes rough running and possibly the noises we are discussing). The external leak is from the rubber o-ring and it seals the "pressure valve holder" to the pump body. The second type of leak is leaking the pressurized fuel from the line back into the pump cavity. The parts blow up shows these parts in this linear order: 1 - pressure valve holder, 2 - seal ring 017 997 41 48 (rubber o-ring), 3 - spring, 4- seal ring 004 997 45 40 (brass ring), 5 - "pressure valve", 6 - pump element.
The leak, that matters here, is above the valve and inside the pump body, below the pressure valve holder.
Sure could use a picture.