I bought on Ebay 4 injectors seals for 2.5/2.8 CRD 2002/2007.
I saw that one side of the seal is totally flat, the opposite side is a little rounded: which is the right side towards the injectors (facing up)?
Thanks

 

I've changed mines, a couple of them twice, but never noticed. The two mating surfaces must be approximately the same so cant see it making much difference.

Just went out to the car (I keep spares in it) and the washers I've got are flat both sides.

Did you get new o rings too? If you're changing due to exhaust fumes inside the car, it was the o-rings that were away on mines.