As the injectors are very expencive there is a few Bosch Diesel centers that actually repair these injectors, both totally rebuild and only repairing the return fault. That is if they have the equippment to repair and test injectors - it might be a very reasonable price to get it fixed.
We have one diesel center here that have parts in stock for repairing this at a fraction of the cost for even a overhauled component from Bosch.
And aint it strange
that it seems to be the german parts failing in these diesel engines
I dont know about the TDC in the dCi but i replaced TDC for a new genuine one on our Scenic 2.0 16v as a precaution when i bought it, and that was made by Siemens.