Yes, that is correct now I think back. The seal actually seals onto the crank pulley and not the crankshaft. Have you taken a look at the pulley and the actual shoulder on the pulley for scoring/ roughness to see if it might be tearing the seal?
Was the timing chain kit genuine Ford, or one of Ho-Chi-Min's imports? Might well be a poorly machined lower sprocket as you say.
What does the pulley look like when the van is running? Can you see any obvious runout?
I have booked it into ford however they are very hesitant to even look at it, so really not holding much hope.
Tossers! They tend to abandon their vehicles once the warranty has run out.