I decided to renew the pinion oil seals before refitting the prop shafts on my rebuild,

I bought a pair of https://www.ebay.co.uk/itm/181190755073 (part FRC4586G), removed the flange from the rear diff and started to prise out the old oil seal,

However, the old seal wasn't the typical C-cross section rubber style - it was a U-cross section metal seal, with a dense fibrous material within the U. I only realised this once I'd already bent it and found it wasn't going to easily pop out.

So after a lot of messing about trying to shift it, bend it, prise it and loosen it, I managed to get it out. The new one seems to fit OK, but I'm puzzled why it was a completely different design. Have I done the right thing by replacing it, or should I have left it alone? Is the metal-style just an old design or have I got the wrong type of replacement?

I was going to check the front one, too, but couldn't shift the castle nut, so I think I'll leave that alone for now. The engine is already in, anyway, so I've already knobbled easy-access to the front. Should have done it a while ago, but can do it later just as easily, if it shows signs of weeping.

Yep, the good old metal and leather oil seals, your new rubber one's will
work just fine as long as your flange isn't badly worn.

50 years is the difference between the seals

Ah, it was leather?! That makes sense, I guess...it broke up as I was trying to get it out, but it seemed more robust than I would have expected felt to have been...which is what I assumed it probably was. I suspect the leather was past its best.

Is there an approximate year when the seal design changed?

Let's hope 50 years will be a step in the direction of reliability rather than just cost!

Thanks for the info. I'll relax that I *have* got the right seal fitted now, then.

As a matter of interest, is there a 'right' way to remove them, rather then the really messy hack I was doing?

There is a neat tool you can get (not expensive) with a hook on one end which you
push through the rubber or leather and at the other end is a piece sticking up that you
hit with a hammer and it knocks the seal out, simples
If by chance you buy a seal and it is a metal & leather one you need to soak it over
night in gear oil to make the leather supple,