TD5's are great engines that are massively detuned from manufacture. Earlier ones had plastic "pegs" to locate the head, these were prone to movement. Responds really well to an ECU remap
Check the loom from engine to ECU, oil tracks through it I think plugs to check are blue and yellow. The thin oil tracks across and causes poor running. Easy cheap fix.
Apart from the usual chassis, outriggers, cross member rust, they are a bomb proof motor.
Bin the EGR and CAT, get a remap and bigger intercooler and enjoy a life of driving a colander