If the fluid looks decent, just change the filter. I have split many a 555 mainly to replace a broke flex plate for the torque converter. Worse part of the whole deal is those two little bolts on bottom of fuel tank that are vertical and screw up into the tank. The rest is just bulk work. That was before flex head ratcheting end wrenches were widely available. Probably 20 years ago. I had a deal with a heavy equipment company. They provided me with an international service truck. 16 ton auto crane, hydraulic air, welder, torch, recovery tank, rigged out good. Deal was, I had to go do all their assigned work. Then, when off, I could take the truck and use it like it was mine. Parked at my house every day. Worked the Little Rock area.