Fusion 1.4 Tdci Slight Engine Shudder

A few months ago I bought an 07 Fusion TDCi with only 9,000 miles on the clock. After a few miles it developed a slight engine shudder when accelerating or under load up hill. It was so slight at first as to be almost un noticeable, almost like driving over a slight bump in the road. This became progressively worse and more frequent, rather like a miss fire. At times I could drive 50 to 100 miles and it would noit do it then it would do it half a dizen times in the next 10 miles.. It was very bad after being stuck in stop go traffic in a motor way hold up. When the hold up cleared it was very jerky when accelerating for a short time then cleared and was fine again. At one point when it was doing it quite badly I depressed the accelerator fully and nothing happened. The fault then cleared and the engine ran normally. While taking it to be serviced the engine lost most of its power and the amber engime warning light came on along with the red led. Due to lack of power it stalled going up the kerb at the Ford dealers. When I restarted the engine and bumped it up the kerb the fault was gone and the engine reved up normally. The Ford mechanics could not find any faults and reprogrammed the injectors changed the filters and blew through the fuel lines. Computer diagnostics came up with nothing. When I drove home I noticed the jerking under acceleration was still there. The following day it started and ran very roughly , 100 yards down the road the power fell right off and the alarm came back on. I drove it slowly back to the Ford dealers , who eventually diagnosed a faulty number 3 injector, with excessive spill back. Now I know how diesel injectors work and I don't see how a mechanical device can work one moment and not the next, either they work or if they have a fault they don't .It is not something that can cause the symptoms I experienced. During the 9 mile journey home the fault was not evident. So maybe they were right and have fixed the problem. We shall see. Have any of you other 1.4 TDCi owners expeerienced anything similar? .