Power steering pump leak 300tdi

I have found a thread for repairing a 200tdi pump but nothing for the 300 and the PAS pump on my 300tdi is leaking badly from what seems to be the mating faces. I have found a seal kit at Paddocks but it looks to be just a seal ans a large O ring. I haven't taken the pump off yet so not sure how its assembled but there seems to be the edge of a mating gasket visible between the faces of the pump and and the leak is from these faces at the lower edge. The paddock kit has no gasket so not quite sure how that works.
Is there a mating gasket, or is the large O ring in the kit for sealing the housing? The pump is otherwise fine with no noise ( when its got fluid in the res) and no steering judder. Can it be repaired, is it worth servicing, or at 17 years old should I simply replace it?It has to come off one way or another so if I can save a few quid for a bit of extra work its a good trade off. Any repair advice please? thanks

Just replaced mine on my defender for the same reason as you, got an oem one from paddocks they aren't too expensive and the original lasted 17 years so this one might too!