The thing you are forgetting paul is, when ford fit bits together they are done with new bits which are corrosion free no distortion at all.
As some cossie are now over 20 years old this will not be the case.
If it takes a bit of sealer to stop a leak, what does it matter, surely it is better to stop the leak rather than have a leak just cause someone doesn't like sealer, or because ford did not use any.
Ford don't always get it right, like the almighty cock up with cossie cooling systems, which they rejigged with the 4x4.
Rolls Royce use sealer on BRAND NEW JET ENGINES, as do USAF on fighters, with brand new components.
It would be intersting to see how a sealer can cause leaks, most likely the leak was there to start with, hence the sealer, and the sealer failed to cure it!!
tabetha