It seems that you have the infamous DV6 engine .
When the injector seals go south hot gasses from the cylinder make their way to the valve timing area (no gasket between the cylinder head and its upper part ...just some silicone !)http://www.motor-talk.de/forum/aktion/Attachment.html?attachmentId=685547
You can imagine the result ...http://www.theturboguy.com/uploads/1/0/3/5/10358883/api-presentation_1.6_hdi_carbon_issues-3-2.pdfhttp://images.forum-auto.com/mesimages/511236/Fuitejointsdinjecteursexplication.jpg
Usually injector seals failure manufests itself with with some gas/oil leak around the injectors(lifting the plastic cover at least once a month is a must here).The sooner you catch the problem the better.
Althought this may not be the case here, I'd have it inspected ( dropping the oil pan-preferabley- or removing the vacuum pump would tell if there was any deposits)...
There is plenty of info about this design flaw affecting severals brands using this engine...
Why was the oil pickup replaced anyway? I hope it was not an attempt to get rid of the deposits caused by injector seals failure...it would take greater efforts to do the job.