The part in your picture is the Wabco brake vacuum pump, the oil leak is a common problem caused when the rivets that hold the body sections together get loose.
You may need no parts other than a new gasket for the pump to engine block joint and some M5 set screws and nuts, remove the Vac pump from the engine and drill out the rivets one at a time systematically replacing each rivet with a small nut and bolt with a lock washer,on mine I think I used M5x12 hex set screws and nuts. With the nuts and bolts tightened up you will find the pump head joint leak will cease, replace the pump onto your engine.
You can of course buy a new pump, not sure how much they are in UK but the genuine Wabco is rather expensive here in Australia.
The way that oil is pooling at the bottom of the lower welch plug looks to me like the replace-the-rivets trick might not fix it. These things seems to leak from every flippin' oriifice!
The way that oil is pooling at the bottom of the lower welch plug looks to me like the replace-the-rivets trick might not fix it. These things seems to leak from every flippin' oriifice!
I would say so. Unfortunately the replacements tend to fail as well at some point, but at least you will have had the practice in getting the bl00dy thing off!