[rha478]

I changed my oil in my truck 4 days ago. I was reving the engine up by the throttle by the injector pump, when I noticed puffs of black soot coming from the down side of the turbo. I put my fingers down their and felt exhaust coming from that area. My question is: is this hard to fix and can I get a gasket from the local auto parts store? Have I done any damage to my engine by not finding this earlier?