hi ive a 2000reg d22 ,2.5 tdi .i came out thismorning it had a real hard job to start turnt over lots when it did start lots of blue/white smoke drove 10 miles to work starts perfect just now ,would i be correct in thinking glow plugs are worn ,how hard of a job? do i get genuine nissan or would motor factor one be ok ,thankyou for any help ,cheers norm