My 15 ES exhibits a similar problem. 5th gear comes and goes on the display. I removed the sensor and cleaned the contacts. Worked for a month or so, now blinking on and off again. I wonder if the spring tension on the small plunger is insufficient? I may try to stretch the spring a bit? If that fails, new sensor I guess. Although, I know when I'm in 5th, don't need the display to tell me. But, I am somewhat anal, and don't like things not working.
I spent most of my money on guns, motorcycles, women, and whiskey. The rest, I just wasted!