I guess could be your rubber seal quality with high shore hardness I suppose. If that's the case suggest using flat washer in between, prior to arrest the leakage issue for the time being.

Lip seal with soft rubber, e.g. Linatex will be a good aid. A fancier solution would be a double lip seal with water purge in the middle. Typically replaceable stainless steel ring is used as counterpart.

Before start engineering for these "aids" you may want to double check the ball mills operating point, i.e. volumetric filling. If the mill is overloaded, or does not have sufficient gradient (feed opening smaller than discharge opening) no seal arrangement will save you.

Yes the mill is almost running with double its capacity (Rated 30TPH, running with 55 TPH), earlier we used to have Linatex seal wiper and SS seal ring. In this course Linatex seal wiper didn't give good life and within a week the leakage used to start again, hence we changed the MOC of seal wiper to conveyor belt MOC. With this we are getting a life of about 15 days. Now the condition is the SS seal ring getting worn out very fast. This we have replaced with hardox seal ring of BHN 500, let us see how many days we get the life.