If I had to guess, I would say your problem has to do with electronics...either a solenoid, relay, or maybe even a broken wire somewhere.
I also have a intermittent issue that is kinda similar on my 2001 75XT. A few weeks ago, I was using my machine at a friends house. I shut it down for lunch for maybe a couple hours. After I got back in it, I couldn't curl the bucket. I could move the machine, raise and lower the boom, but I had no bucket curl. The right joystick was physically locked out (I could still drive forward & backwards though). I messed with it for a minute, shut the machine down and restarted it. Same thing. I opened the fuse box to the left of my seat and wiggled the relays and wires. Then waited another couple minutes, and it started working again.
Are your joysticks locked out, or do they still move but the machine doesn't do anything?