I think I can match the diversity of the gearbox oil leak through the driveshafts described above.
I bought 4376R and 4688R in pieces in a 40ft container via a dealer in Chicago who died, the whole lot went to a dealer in Houston, who also died, his widow sold them to an enthusiast in Louisiana who decided it was beyond him, so 4376R, 4688R and a whole load of other stuff, the good, the bad, and the ugly, was shipped in a 40ft container via New Orleans and Southampton to me.
I have completed 4688R which I am keeping, and I am finishing off 4376R at the moment. I put the gearbox in, drained and filled it with oil, and oil poured out of the diff output holes, both sides.
I thought putting the driveshafts in would cure the leak so set about getting the shaft splines lined up to bash in the roll pins. I check the holes are lined up with a 5mm drill. If that goes through and there is no inward play when I take the drill out, I know the shimming is correct.
The shimming was awful, so I went on eBay and bought loads of shims. £3.69 for 10. Cheap. I will have 10 in all the sizes please.
The shims arrived, and it was time to add more shims to get the play out before driving in the roll pins.
I thought I would see how big the gap was by undoing the big castellated ring thingy, and it was f'ing huge. 10mm. Something is wrong, all I could see was a rubber O ring.
I then undid the castellated ring thingy on another gearbox and saw a splined spacer covering the O ring. This spacer was missing on both sides on the gearbox which fitted 4376R.
Luckily the container came with a spare 4 speed gearbox, so I went to get the spacers out by undoing the castellated rings. They were f'ing tight. I have the special tool from Banks for undoing them, a 1 1/16" ring spanner to put on the end , a big hammer, so I started undoing the ring thingies. After about 1/2 a turn, they are normally easy to undo. This one was very tight, I put heaps of pressure on the ring spanner, bashed the spanner with the big 2kg hammer, and "Ouch". The spanner fell off and my head went straight down on the the selector rod on the end of the gearbox, and then my head started leaking. "Ouch" was not enough, time to go and clean up the wound.
I stopped the bleeding by pressure on toilet tissue on the wound. I summoned the courage to look in the mirror, took the tissue off and there is a Mercedes 3 spoke star right between my eyes. I looks like some sniper has assassinated me. Time to fit an Elastoplast.
Anyway, I removed all the shims, fitted one splined spacer, mastic on the ring thingy, tighten to the same place marked with a dot from a centre punch, fit the lock tab, line up the splines and the holes in the driveshaft, and with zero shims, the holes align exactly. Drive in the roll pin, and all looks fine.
So the oil leaking out from the diff output shafts was because the 10mm splined spacer was missing so the oil seal in the castellated ring thingy had nothing the seal against.
Tomorrow, the other side.
I now have to go down the pub with a plaster on my forehead right between my eyes. That will take some explaining. Taliban assassination attempt maybe.