Hello Max, as no one has yet answered your question, I thought to jump in..... If the grey seal you mention is that which sits in the tube from which the arm of the mirror can be extended or retracted, it seems to be a very common issue with the mirrors with extending arms. a few tears back I changed my mirrors and bases for new ones with circular convex mirrors to give a wider view... I just went out to my garage and both the white shaft seals have the same split in them.... Not that it causes me any concern....
Of course I may have misinterpreted your issue, and just caused some degree of confusion, if so, I apologise.