I had kind of the same problem earlier this year, here was deal;
Both cables (left and right steering cables) are ran through the same tubing. The tubing looks like hydrolic line, very stiff, and crimped on the end, that went into a cylinoid. The cylinoid has a bar on it that is connected to the motor and does the actual turning.
The tubing had a really sharp bend in it, where it came out of the boat and connected to the cylinoid, real sharp. Over time, the cables began to fray and pieces of the cable were rubbing had on the tubing until finally, the cable broke.
I found this out upon disection of the cable. The reason it would turn right smoothly was because the frayed cable was going with the tubing. Turning back left, the frayed cables "dug in to" the walls of the tubing at the sharp bend.
Does that make any sense?
