Cat C15 clogginf fuel filters

I have a 2006 Pete 389 with a c15 in it. when I came to work for this shop they told me about the problem. I finally cut upen the primary and separators and found a black oily looking/feeling fim coating the filter matter. this truck has had chronic hard starting issues as well. I removed the tanks and had them cleaned, and removed the lines to the engine and cleaned them out as well, and since doing this 2000 or so miles ago, the truck returned to the shop with the same oily/black slick on the filter matter inside of the filters. We have also been treating the fuel with bioshock because Cat told us it was an algea problem.

Any help greatly appreciated.

thank you and happy TG!

 

to me it seemed like engine oil. I ran the tip of my finger through the filter element and came out with enough of it on my finger to coat something the size of a ritz cracker.

 

I appreciate all of the replies. I left out a few particulars during the original post. I have about a dozen trucks in my fleet, IH, Petes, and one FL and a few straight trucks. this is the only truck with a problem, so I can only assume he got a dose of bad fuel at some random fuel stop. I removed the hand primer a couple of weeks ago because during it's ritual morning no start, the primer has gotten worn out/damaged. It was so bad that it wouldn't seat down inside of the bore. When I removed the primer, I was immediately taken by the fact that it was all black inside, so that's when I decided to open up filters and take a peek. I also felt around the inside of the fuel tank looking for a slick that I have found in the past on a lot of Detroit powered trucks.. none! That's why initially I was in debate over the cause of the filter sludge. Cat was called about the issue and they said it can't be oil and was probably contaminated fuel. I'm guessing whatever is contaminating the fuel could also be the reason why the truck doesn't start after it's been sitting a while I suspect the bleeder valve in the primary housing to be the problem. In all of my years dealing with C15's this is only the second time I've had one having no start problems and the first time turned out to be that little valve bleeding off.

Thanks Gents! Hope your holiday was great!