Crankshaft seal (transmission end)

Hi
I'm just changing the clutch on my k11 1.0 I found the sump was leaking at the transmission end which I've now sorted. I bought a new crankshaft seal from the Nissan dealer which measures 104mm across 84mm diameter in the middle and 8.4mm depth. When I took the old seal off its the same diameter but the height is more 11mm. Phoned up Nissan dealer today and they say it's the right part? The old part no was 12279-2F000. New part is 12279-3TSOA. After googling the old part number I've found that it's not in production anywhere. If I fit this new seal there and fit it flush like the old one there seems to be a bit of a gap behind. Would it make much difference? Looked at eurocarparts and they have an exact match same diameters and the right depth. Anyone had this problem before
 
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