An EGR is an exhaust gas recirculation valve that attempts to recirculate crankcase fumes but eventually gets bunged up with tar.
A DPF is a diesel particulate filter designed to 'contain' hydrocarbon
particulates on start up then burn them off safely once the engine gets hot. Unless the DPF is heated directly, this doesn't happen when the diesels are used for short runs from cold and in some systems the extra fuel fed to the engine to assist DPF regeneration sinks into the sump, raising the sump level to a point where the engine runs on its lube oil. More here: www.honestjohn.co.uk/faq/faq.htm?id=113