Whats the difference between the FD 4609 and the FD 4617, they look the same to me.

 

FD 4609 was the old style.

 

I did mine tonight and had the 4609 in it and replaced with the new 4617 but it is different physically. Does the frame rail filter cap mount flush to the housing or is there a little gap? I was worried it wasn't seated properly as the 4617 filter is longer.

 

still flush when you tighten the cap. New style has the additional o-ring on it so it is a tighter fit.