No RWD. I need advice please.

[Rod.]

Got the word today from the mechanic that their testing why I have no rwd shows the solenoids are working so he suspects the "viscous coupling has failed inside the tranny". the car has 170,000 km so just over 100,000 miles.

I know nothing, so am looking for advice.

Is it necessarily the transmission, or could it be the TCU?
If its the transmission, is there something other than the transfer clutch assembly to suspect?
If it's the transfer clutch, is this a major repair?
In terms of the lower cost, should I be thinking about a swap or even going for a manual transmission?

Thanks,
Rod.