VLSD...What do look for?

[tfj]

so i'm taking a trip tomorrow to go look at a used VLSD that i'm thinking about buying. is there anything that i should look for? any big things that mean that the diff is busted? it's supposed to be a stock R200V from a S13 (SE model), and it's going on my '91 S13 (base model), so hopefully it should bolt right in. i'm just kinda worried that i'll get it and find that something is horribly wrong.

thanks.

[C-Kwik]

Try turning the two output shafts in opposite directions. If it's loose, it's an open diff. A VLSD will be very hard to turn in opposite directions.