S600 & CL600 with 137 engine - timing issue
 

The car is self-aspirated CL 600 with M137 engine year 2001 V12 - and it has low milage 100.000 only. https://en.wikipedia.org/wiki/Mercedes-Benz_M137_engine

It had oil leak and missfire issue and I opened the engine. Noticed that the timing is not fully OK. The driver-side (left) bank's camshaft is some 3 mm too much ahead from the timing mark towards clockwise when looking from the front. Crankshaft and right-hand bank's camshafts are both at the their marks correctly.

When assembling all, I cannot get the left camshaft rotated that 3 mm backwards, because the sprocket is connected into the hole in camshaft and the camshaft has the chain towards the crankshaft....even if I loosen the bolt of the camshaft sprocket a bit. Should it turn backwards to get the timing exactly? Or shall I just leave it as it is?