Raise the forks to a point where it's comfortable to work on the reach cylinders. Drape something over the forks so that nobody walks into them.

Extend the reach and unplug the battery. Then cut a 2X4 or 4X4 to a length that you can use to keep the reach cylinder from retracting. Hold it in place on the side opposite the cylinder you want to work on and have someone pull the reach lever to retract. (with the battery unplugged!) Gravity should bring the reach assembly back against your 2X4. If it doesn't you may have to give it a little push.

Once the assembly is blocked out, you can put a pan underneath, disconnect the hydraulic lines at the cylinder, and remove the mounting pins. JIC plugs and caps will keep oil spills to a minimum if you install them on each line and fitting as you disconnect them.

The important point is to have the assembly securely blocked out before you stick your fingers inside. You could even use a chain to hold it extended if you can find something to chain it to.