Dave,

There isn't much you can do with a knackered viscous, apart from replace it or....if funds are okay buy an upgrade "clutch plate" type LSD for the cossie diff, which last longer, can be adjusted and can be rebuilt with new clutches when they're buggered.

I'd avoid a s/h viscous they are all usually knacked or don't last long.

As for the paddle clutch, its like any clutch, with naff / animal driving it can be worn out very quickly, but with decent launching technique and no abuse they are fine, as James said.

Cheers Dave