I thought you had the rear axle out of a 90 series with rear disc brakes?
I do.
Handbrake still uses drums, just like most other larger Toyotas.
90 series uses the same axles seals as we did from the factory, same sealing mechanism.. same potential to leak!
Good new is, it definitely WAS oil contamination, but there was no sign of a recent leak, so I cleaned it all back, reused the shoes and put it back together. Handbrake now works as intended and seems equal across both sides (that's part of the test, on a brake roller)
I'm not sure why there would be oil contamination in there and no obvious leak (I assume it was axle oil) it was a tiny amount, just enough to "lubricate" the shoes. I'm guessing it was either from assembly (I use trans oil to lube the sealing services on the axle seals) or a bit leaked out when the oil was extra hot due to running in the new ring gear and pinion, on a new seal. (Yet all seals are new, if one was incorrectly fitted or damaged, I'd expect to see a lot more. Breather is new too)
I don't like the fact that it happened as I don't believe things "fix themselves" but I deliberately didn't fit my new shoes, so I can pull it apart in a couple of months and see if there is any more evidence of a leak, now I know its all been cleaned up. When I do I have some more parts to fit (new bell crank, pin, boot and bracket to cut down some lateral play in the mechanism) I'll fit the new shoes then.
The only other things I can think of are:
-Some of the copper slip I used on the moving parts degenerated and ran
---Unlikely, it didn't look like it and copper slip has a distinctive look, I'm very careful when putting it on, plus that's thermally stable. It generally doesn't really happen.
-The "oil" contamination was actually brake fluid, from bleeding.
---Possible, I didn't sniff it, but and dirty trans oil when its just a residue looks like dirty brake fluid. (there was only a very small amount in the inner mating face of the disk) If that is the case I'd have expected deterioration to the POR15 finish.. (I know its good.. but brake fluid good?)