Series 3 Rear Diff Pinion Seal

I am currently removing my rear axles to weld on a new diff pan, and replace the suspension springs. At the same time I will replace the pinion seal as it is leaking. from the research I have done either frc4586 or frc8220 will will be suitable for a '82 SWB Series 3 (please correct me if I am wrong). As there is very little differance in price and whatever I get will be OEM I am wondering if there is any differance and which one of the two is preferable?

Is it the oil seal or the metal seal?

I can only see FRC4586 in my parts catalogue for standard Rover axle.

either or ,i tend to fit frc8220

James is it the Viton version that you use seems they are longer lasting?

jamesmartin said:

either or ,i tend to fit frc8220

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Well that has added a third option!
If that is the one you use is that the best option which will last the longest and hopefully keep it "oil tight"? I haven't ordered the parts yet and am happy to spend on a quality OEM item as I don't want to be doing it again any sooner than I have to. Or if there is no discernible difference when fitted I will just buy which ever seal has the cheapest OEM version.