as we "SHOULD
" all know that the only cause of contamination is via engines or apu due to leaking oil seals( apu less likely) then as
applevid has said maybe maintenace practice is the cause but i doubt it as no other eurpoen airline is having such great numbers of events.
might also be down to engineers not recognizing the tell tale oil stains or choosing to ignore it - which knowing a few UK CAA engineers i find hard to believe