If you had the Centa fitted to a car that originally had the Harley type compensator you will have hole in the housing originally intended to grease the compensator. A borescope through the hole will allow inspection.
Not 100% true as a few cars have no hole at all....early HD drive cars especially as no grease nipple ever fitted. Had cars with Centa but no hole as well.
And as Javier says, you can see the ends of the Centa rollers with a borescope and no more than that.
And I doubt the dealers used a borescope to look (as its quite fiddly) - just a pen - to tick the service sheet box as 'checked'....
I find the silicon has normally disappeared by 1000 miles....
