while I was replacing my water pump on my c-15 cat,i found gunk in the end of my oil cooler.Does anyone know what it is?

ok,I found out what it was..tks anyways drivers

So what was it? Don't leave us hanging in case another driver runs into this and wonders the same thing!

it was that stuff that is in between the tubes in the oil cooler.I changed my water pump and I thought it must have been something else like some old stop leak someone had put in,but it was ok.We cleaned out the loose stuff,put it back together and the truck is doing great!