Where's all this frikken oil coming from?

I have before me a Crosman NP break barrel rifle that is blowing oil (or some kinda black crap) out the transfer hole. About every 30-50 shots accuracy goes to hell and it will deisel and go off like a .30-06 unless I pull about 10 dry patches through the barrel every 25 shots. The first time it did it I almost crapped my pants and my ears rang for an hour.

I haven't over oiled it, the only place I've ever put any oil is on the hinges, and on the trigger when I did the trigger tune up. But I promise it was very sparingly.
How can a barrel get so oil fouled so quickly? Where is all that crap coming from?
 
Something that might be contributing is a nick in the piston seal that is letting lube get into the compression chamber. If it were me I'd order a replacement piston seal from Crosman or an aftermarket supplier like Vortek if they carry them. If you do tear down the gun, make sure to deburr the cocking slot so as not to have the sharp edges cut the new seal on reassembly.
How long have you had the gun?
 
"JohnL57"Something that might be contributing is a nick in the piston seal that is letting lube get into the compression chamber. If it were me I'd order a replacement piston seal from Crosman or an aftermarket supplier like Vortek if they carry them. If you do tear down the gun, make sure to deburr the cocking slot so as not to have the sharp edges cut the new seal on reassembly.
How long have you had the gun?

That was what I was afraid of (blown piston seal) but when the barrel is clean it shoots good.

Guess I'lI find a place to order parts and overhaul the blasted thing. I have a Gamo that needs one too so I might as well do that one too while I'm at it.
Sonuvabitch! Always something!