I'm about to dive into my first FWD timing belt replacement. I've done RWD's several times over the years, but had a couple questions. My guidance is a Haynes manual that makes it all sound fairly straight forward. I plan to replace the tensioner and idler at the same time, along with the serpentine belt. I have not looked at the cam sprockets yet, but according to Haynes there should be very finely scribed index marks on the sprockets. If this is true, why does everyone make it sound like it's imperative to use a cam locking tool like the four-legged device that IPD sells? When the tensioner is relaxed, do the cams "spring" forward or backward causing valve/piston contact? If I find a leaky seal, my understanding is that I then need to secure the cams at the opposite ends so that I can remove the sprockets and not lose my reference. Are the sprockets not keyed to the cams? So let's say the seals still look tight yet everyone says I need to secure the cams before removing the belt - what tool is recommended? IPD gizmo? Homemade? And if I have to secure the opposite ends of the cams to remove the sprockets, what tool is recommended?