Mine is also 8 and he has it in his off hind hock. The vet also thought he might have it in his front coffin joints at Christmas but all seems much better after liberal doses of newmarket joint supplement.
I was told it was unusual he is 13 now and on but all the time Do yours often hold up the affected leg? He has also just got it in his hock on his other hind leg
4 in her coffin joints - now just turned 18 & it's pretty much everywhere but she's had a good innings, she's only just starting to feel / act her age.