Power loss on 2006 311 CDI H/R LWB 190Kmls?

Reguarly serviced 311 seems to driving as naturally aspirated..has speed range but lacks acceleration. At last 2spanner service was advised slight leak on flexi-link on exhaust..is this connected ? When pedal floored no real oooomph..and continually having to change down to negotiate hills (loaded or unloaded). NO excessive oil consumption