http://members.boardhost.com/ukautotalk8/msg/1414012450.html 
on September 18, 2015, 9:28 pm, in reply to "Re: Citroen C5 - Turbo charger failure, Very high engine oil level"
>>>Do i still RUN AWAY from this blasphemous arse?? <<<<
Yes !!!
A good flushing agent wont fix this, it will just loosen the crap and compound the problem.
removing the gauze may increase life of new turbo, but it almost certainly will still fail within the warranty period due to to carbon deposits scoring shaft.
Removing sump and rocker box for inspection and cleaning is also a must.
Any sign of leaking injector seals ? often blamed for causing carbon issues
To be honest with dubious service history and customer being evasive with simple questions I would advise running away.
If you are a gambling man there is a UKAT member selling a H/D inline turbo filter for these which may increase your odds a little.
Cheers Aidan
