I am wondering if they are lacquered or have a type of protective film on them and have water / oxidisation under it.
I am guessing you will wreck them by trying to remove them and working on them on the car could damage the area around them even if tapes off?
I may be tempted to see if you can replace.
If you can get them off or work in that area paint them or strip them and metal polish them back and re seal?