||The viscous coupling is a sealed unit, if it is damaged, replacement is required. This part will be needed if your diff limited slip isn't functional anymore and you have a single tire spinning.
Parts such as bearings and seals are commonly available, the TT stuff is a bit pricy.
I frequently remove stock LSD carriers during upgrades, I likely have a couple viscous coupling units around.
Parts and labor are hard to estimate, depends on what's going on.
Are you having gear noise, bearing noise, leakage, excess gear lash, or just a non-functional limited slip unit?