Hello, it would be best to have a vet (or usually I ask a farrier out first ) to come and look if there is something inside the horse's cut or if it's an antibiotic need or actual lameness.
It doesn't quite sound like it's actually healed . (does this area look like it still needs to heal or is he reopening it before it can?
If so,consider keeping him more contained /quiet so he can heal.
You say it's oozing but not if it looks infected.It sounds like you have the right support system going on for his ankle.
Also,be sure your horse has had it's shots,especially tetanus.
Articles & News: How To Prevent Your Horse Going Lame From The Most Common Cause Of Lameness - Pets
Let me know if you have any other questions.
Happy Trails!
Thankyou & God Bless!