Not sure why car is running so well, injectors going open circuit we have seen before, we have replaced bent con rods and damaged pistons before, the last car we did was a facelift TD5 2002 model year, full dealer history ( For what that is worth ) and had only done 23,000 Miles
Injectors are coded in and need specialist diagnostics to do them ( Test Book, rova com ETC )its easy with diagnostics to see which injector is at fault.
I would start with diagnostics DTC's etc and go from there, at a guess its a injector problem possible two and always replace the injector loom and seals for what it costs