My buddy changed the hydraulic system oil on his 1994 Kubota L2900. He just bought it within the last year, and he thinks the system oil hadn't ever been changed. It took 10 gallons of Kubota Super UDT oil at $30/gallon. He was shocked at some of the debris trapped in the filter magnet. Two pieces an inch long look like parts of a piston ring.
Tractor has always functioned well, but it seems amazing the debris isn't from something important to function. Could it be that these remnants were left in the system from the assembly process? I've heard other stories of much debris in hydraulic systems, but it seems amazing that any debris that looks like parts doesn't cause a malfunction.
My buddy was looking at his service manual to see if he could find any parts that look like the debris in the parts breakdowns. He found some "synchronizer springs" that look like where the debris could have come from. He said it shifts perfectly which makes it amazing these parts aren't essential.