Most if not all No.8 butt plates will turn to caca over time.
You can get a hard resin replacement at Vintage Grips in FL or I believe Brian Dick also has/had some.
The repro's are a good copy and worth the money. If you store your No.8 rifles vertical on the butt plate most will break up over time
Good point Warren, i store my No8s & No5s muzzle down for that reason.