Just because the idler pulley has exploded and the belt is missing, it doesn't mean the SC is in need of overhaul.
The SC has oil in it and is protected from the elements, so the bearing should last a heck of a long time unlike the regular greased ball bearings of the idler.

My guess is the previous owner just didn't care much about maintenance or have the money to get it done, so when the bearing exploded and threw the belt of he just ignored replacing it.

I would just turn the SC by hand and see how it feels - unless it makes any weird grinding or clunking noises or feels off, i would just give it some fresh oil and throw some new idlers and belts on the engine.
(just remember the coupler is spring loaded, so take that into account on how it feels to turn it by hand)

 

Elite Jaguar and Land Rover in Stockport / Manchester (England) put on a new idler and belt. I got lucky, the car is now sorted power wise. Just the rumbly harsh ride to sort out next then, then the misfire, plus the slightly odd smell the interior has. Funnily enough I think my old 1997 X300 had the same whiff. Probably decaying headlining foam.