Intermittent poor starting with TD5

Hi there, my 2004 TD5 has recently developed intermittent problem with starting with engine turning well on starter but not firing even if at operating temperature. This may happen a number of times then start and be fine firing up for a while until the problem returns. Once or twice it has fired then stalled after a few seconds. Have noticed that the engine check and glow plug dashboard lights do not show when it fails to start. Have changed fuel filter, cannot see any fuel leaks. Any advice would be gratefully received.

Injector harness, oil leaking into ECU? Check the plugs going into the ECU, is there any sign of oil?

Thanks for the tip, have checked the ECU, no sign of oil on plugs but will investigate electrics further today