Done it by removing fan and loosening housing, no need it or cooler right off. Check it's not the pressure switch leaking - pretty unusual for the cooler seals to leak, if they are it'll be peeing out under pressure.
I had mine off when I forgot the tin that fits near the cooler when I did my recent engine out and clean up. I dropped the heat exchangers to get the fan off. Had to remove the cooler to fit the tin. I didn't replace the seals as they looked in very good condition. I know I should have but I didn't have any replacements. I would remove the fan casing fully, then you can get at the cooler, you are sure they are leaking? It's a lot of work otherwise.
