seemless planes

Hey,
i have 3 planes as a background,
dynamically moving to form an infinite background with the possibility of multiple textures like:
(letters being different kind of textures)

A
A ]plane 1
B ]plane 2
C ]plane 3
C
C
C
D
E
E

which works. unluckily the planes are not seemless
screenshot:
http://s7.directupload.net/images/131130/5y6zq53k.png

any ideas what to do?
is there a shader which helps me to avoid this?

 

seems to be a general issue with the default shaders:

http://s1.directupload.net/images/131130/jsk8i5w8.png

i'm using additional planes for the border-elements over the background