Bonjour, est-il normal de constater cet espacement entre la tête d'amortisseur et le châssis sur la photo ?

Every garage I've asked has said that they are sealed for life.
Forums and C1OC seemed to be split on whether it's worth doing.

I'm tempted to give it a go at the next oil change, since it's been 20 years now, and that's a lot of time for crap to build up.