Auxilary hydraulic port leak weird stuff found while draining hyd. fluid

Problem #2 As I drained the hydraulic fluid from the three ports I noticed something black (size of a sick of gum) drop into the bucket from the middle drain. It was soon drowned in fliud. When done draining I poured the fluid through a strainer and was left with many thin chunks of dark metallic junk. When I touched them I could break them into bits. They had the consistency of a wheat thin cracker. I reached into the hydraulic pump through the drain hole and pulled out some more thin chunks. What is this stuff. I would say it was simply sedimentary build up but I drained the fluid one year ago and did not notice anything then. Besides, it isn't powdery, it takes a little bit to crumble it like a cracker. I always thought my system was good. Implements would drop after :30 minutes. Is something going wrong or is it just history showing its toll?