I've replaced flange and seal about two years ago at Chester transmissions.
But it now leaks again. Well, not exactly leaks, but the area is not 100% dry there. I can only suggest to replace everything again.
You live close to Mackie's so you're in great position to do this
They should have flange available otherwise preorder.
I think I'll wait for a serious gearbox repair, remove it and reseal it completely.