Just purchased a 2006 ASV RC60 2350 HRS, Had to give her some TLC and about $4K in parts to get the unit to good working condition. Now that the unit is working I find the boom will not hold position, it creeps slowly down about an inch every 5 seconds at idle speed or full power. Just replaced boom/bucket Pilot control for leaks, note: the boom creeped before I changed the control.
Most likely your piston seals are leaking. Without any test equipment the easiest way is to pull both of them apart
ha, i just bought an 06 rc 60 a few months back. i noticed that my machine does the same thing every once in a while. not very often though. i had wondered the same thing, i figured it was seals letting it leak by. but mine is not bad enough to worry about right now though.