I don't have a manual but I have serviced the Arco 6 winches on my C22. They are very simple and easy to tear down, service, and reassemble.
The first thing you want to do is take a small cardboard box and cut a hole in the bottom of it to fit it around the base of the winch. This will help catch any loose parts that might fall. Once the box is in place, remove the ring at the top of the winch that holds the drum down over the inner works. You might be able to use a small screwdriver, small needle-nose pliers, small hammer for this.
Once the ring is off, lift the drum straight up, slowly. This will reveal the gears and pawls inside. (At this point, I removed the whole works from the boat and did the work on my workbench.)
I can't describe from memory the inner mechanisms of the winch, but the springs and pawls are about the only moving parts inside the winch. The springs are very small and easily lost if you are not careful. I soaked the works in diesel fuel and dried them completely before reassembly. For lubrication, I used a very small amount of the white lube that I use on my bicycle wheel bearings. Some experts recommend marine specific lube, some recommend no lube at all. I don't know the right answer. You might ask this question in the 'gear and maintenance' forum here.
If you don't feel comfortable flying blind on this project, check out any book, or maybe some sailing website, that has pictures/exploded view of a one or two speed winch. Most of what you see will apply to the Arco 6.
Hope this helps.