Mocal Cooler

[cully]

you don't have to keep it, seen them fitted both with and without.

I think my exchanger is allowing oil into the water hence replacing.

You don't have to no bud, but its pretty important to do so. 
Remember its not really a oil cooler as such, rather a heat exchanger. 

Replace it if needed buddy, find them very cheap

Where?

Il do you a second hand one £35 delivered for the oil modine