What is this Box by the Transmission
 

My nephews 1995 850 Turbo seems to have a leak area in front of the transmission. It is all over a black box. We have no idea what the box is.
https://cimg1.ibsrv.net/gimg/volvofo...8dce54bbc.jpeg
https://cimg2.ibsrv.net/gimg/volvofo...078c78390.jpeg

Removal of that cover allows access inside the transmission. Specifically - remove that cover to get to the Valve body. They usually don't leak much from that cover (but it is a really old car) - clean everything off and check after driving where it's really leaking.

lol, that's not a leak, that's rust inhibitor... +1 on cleaning the area as best you can then checking for leaks. Most common leaks are from the rear cam seals (you may want to pull out the air box to have a look around), turbo oil return line (that'll make a huge mess) and on the front side you can have leakly front cam seals. Less common are leaky main seals. The 850s are also notorious for having clogged PCV systems which leads to positive crank case pressure that can push oil out of the seals or even push out the seals themselves. Do a rubber glove test to see if your PCV may be clogged (check for the RobertDIY vids on youtube). Have you also checked your transmission fluid level and color? Its also possible for oil to leak out if the PCV hoses tear etc but its kind of hard to get a good look without pulling up the intake manifold (if you are going to do that, you might as well service the PCV system...).