I've been given a Canon FTb QL plus a bunch of lenses, which have been stored for decades. The foam strip in the mirror box has turned to dust. Is this an easy repair? Everything else seems to work on the rest of the body, so I'm tempted to try a little Canon in my life. Pointers to any online guide would be appreciated. I've stripped Russian lenses before and rebuilt a Zenit 3M, so conceptually I know to use small screwdrivers and not to hit it with a hammer, but I don't want to spend too many hours on this.