rare ,you dont need to pull injectors out ,leak off washer pipes will reuse, rocker gasket will reuse with a little silicone sealant ,you need to torque bolts to 40nm twice as inner will slacken as you get to outer bolts ,then mark a corner of bolt and mark head ,one flat of bolt is the 60 degrees then mark head so you know which bolts have been done as you need 60 degrees x 2 ,then 20 degrees on 10 bolts that surround cylinders only ,if disco rear 2 most bolts need holding up but still in head as they cant be fitted or removed with head in place