Is there any real differece between the washer pumps?

I guest that the rear one should be a little more powerful, but what about the headlamp pump and the windshield pump? Can I use the same if I have to replace one of those? By the way, where can I buy it so they won't rob me?

Don't know about P38s but on Classics the rear had a longer pick up (it poked up through the bottom of the reservoir) so that if the level got low the rear wash would stop while there was still some left for the front. This meant the rear was non-standard, so cost a lot more than the front.
On the Classics they were interchangeable though, you would just loose the reserve.