355, fiberous dust on cam belt

I thought that I had seen a thread on this subject awhile back but I can't seem to find anything in the archives. Upon performing a major service on a 355, I have found this brownish dust that has fibers in it in the cambelt area but can't find a source for it. This dust looks like it could be fiberglass or possibly even kevler. It has coated the cam belts and has built up inside the pulleys for the cams, in the tensioner brgs., and even inside the crank pulley. I have enclose a few pictures that I hope you can see what I am talking about. I have checked over everything in and around the front of the engine and cannot find and evidence of damage. The only possibilty I have found is that there is a cover under the F1 servo right behind the front of the motor that I believe it made from kevlar that was damaged and repaired with fiberglass at a previous time. Maybe when it was damaged some pieces were blown up into the cam belts and chewed up. I don't know. Anybody else seen this?
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Thanks Dave! You are probably right because I replaced an exhaust manifold about 6 months ago. I had forgotten about that.