Ford adopted PSA's Eolys additive DPF system, along with PSA engines with Ford co-produces with PSA (a lot of them are made at Dagenham). The Eolys can last 80,000 miles, but a measure gets squirted into the fuel tank at every fill, so if you fill up frequently the Eolys is used up at a faster rate. When the tank empties it needs to be refilled. But sometimes the tank injection system can fail, and sometimes the DPFs can fail. For the past few years Ford has switched to coated type DPFs, but I can't tell you precisely when or which cars have this. ‘Diesel Car’ magazine has covered DPFs in some detail for a second time.