Rear hub on '85 110

Hello all and welcome to yet another 'damn newbie/blatantly obvious ' question....

After my first off-roading experience yesterday, I noticed this morning a trickle of brown fluid coming from the rear hub's dust cap which had been dislodged slightly. Enough to leave a small puddle on the road - my partner thought a dog had peed on the wheel!

Is this a leak, or does the cap retain a quantity of fluid? If it is a leak, how easy/hard is it to remedy. I've heard that maintenance on hub components can be carried out without the need to remove the wheel as jacking in my street is, well awkward - see avavtar

I'm a fairly competent newbie, but a newbie nonetheless, however, all and any help will be greatly appreciated.

hub seals need changing, the reason its brown is there is rust on the splines and its basically oily rust thats leaking out, check the splines on the drive flanges and shafts while its apart, they have a nasty habbit of wearing