12 Fiesta DSP6 - h171

Fiesta dual clutch acting up, been to the dealership a bunch, they keep replacing the seals and clutch assemblies but the trans keeps failing/shuddering.

My mechanic tells me that it needs a new valve body & by now has thoroughly worn clutch plates - ie, time for a new transmission.

What I don't get is how the known problem -- ie, the seals and clutch assemblies led to deeper problems, my faulty valve body and worn plates.

Can someone help me connect the dots?