Binocular eyecups are suffer constant wear-and-tear. After years of use it may be necessary to replace them. Some manufacturers - especially those from the high-end sector - offer a spare parts service for this.
Kowa
Special eyecup for Highlander eyepieces
$ 37.90
ready for shipping in 24
h
Leica
Noctivid winged rubber eyecups
$ 49.00
ready for shipping in 3-5
weeks
Swarovski
Winged eyecup set
$ 42.90
ready for shipping in 3-5
weeks