Is there a specific mileage interval for when this should be done. I have a very low mileage 2008 Gti and during a recent visit to VW dealer for a DSG service they suggested that mine Cam Follower couldn’t possibly need to be replaced.
It does depend...
If running the stock hpfp and tune; The CF should last up to 100k or 120k miles. I personally would replace it at 75k to 80k miles because when the black DLC is worn off the CF's face...more wear is done to the tri-lobe of the intake cam.
If tuned....and the target rail pressure was increased....there will be more pressure applied between hpfp and cam lobes because oem pressure is 110 bar and tuned is usually 130 bar and you would need to check it often and at equal intervals for the moment the black DLC is gone from the center of the CF face. I'll include a pic below.
If the hpfp internals are upgraded; replace every 10k to 15k miles depending on what you learn when replacing the CF. I had to replace the CF every 10k miles at first when using Castrol oil...but since switching to LiquiMoly the CF lasts 20k miles.
Synthetic oil is best...if 100% synthetic. Those labeled "Full Synthetic" are not usually 100% as they can say "Full" if they contain over 50% synthetic.
I do not recommend doing many inspections. Just replace it at a safe interval. Many inspections becomes a pain and you risk stripping the threads out of the aluminum(←because I use US English, LOL) tensioner cover the hpfp is mounted to...even if torqued properly each time.
So again; replace the CF at or before 100k miles to be safe and then, do not worry about it for another 100k miles. If tuned; mileage/CF will depend on the new target pressure for the rail and you'll need to determine when to do the CF. If HPFP internals are upgraded; replace the CF at 10k miles...more if you discover it may last up to 15k or even 20k miles.
This shows the black DLC gone from the face of the CF...time to replace;
http://lh5.ggpht.com/_d1QtJVKjgag/TOqsE36L16I/AAAAAAAAAl4/Cg1BSUCphG0/s1024/CIMG4655.JPG