I took everything apart again yesterday and inspected for cracks. As far as I can see there aren't any. I assembled the filter housing back onto the cooler out of the car to make sure I'd done it right and could see that the gasket was fitted...

UPDATE: I've now got back on this job after coming off shift and a small holiday. Got everything built back up and started the engine to check for leaks and it was worse than before I started. Coming from a different place though so I stripped...

I didn't have any of the right gaskets or O rings for both the oil filters so I've had to order those. The main cooler gasket was leaking from both of the lower oilways. This where I am currently.

I have a box full of TD5 gaskets and seals tucked away somewhere. I need to find it and see what I have. Luckily, I'm not in a rush to complete this job so if I don't have what I need I can order at my leisure.

Thanks Sierrafery. I see no evidence of oil in my coolant but I've bought a complete oil cooler repair kit. Might as well do it for all the work involved so hopefully I'll not be doing it again.

I've had an epic oil leak for a while now and think I've finally tracked it down. I've just done a load of work on the Disco and noticed that oil was pooling on the lip of the block under the oil cooler with the engine running. I cleaned it up...