I've started this as a new Thread, so anyone searching for the Information should be able to go straight for it.
The size of a Freelander 1 Rear-Diff pinion oil seal ( for prop-shaft ).
Is:
7cm x 4.3cm x 1.5cm
So that's the Outer Diameter (OD) x Inner Diameter (ID) x Width.
If you need one you can nip into anywhere that sells oil-seals to quote this size.
I could have used this information myself a couple of weeks ago, so hope it will be useful to someone else.