Rodney makes a note on his website that he has added a rubber boot to the Getrag select cable. The location of the end of the cable, directly underneath the engine vent allows rainwater to drip on the cable. There is nothing to prevent the water from seeping inside the cable sheath because the end of the cable is pointing upward.
The water enters and puddles at the bottom where the cable curves back upward on its way to the passenger cabin. Over time the braided cable inside begins to rust, then fray, and it becomes more difficult to shift. Eventually, it breaks.
In the wintertime, the water inside can freeze. My 87's first cable did that and I had to let the engine run for a little while until the heat from the exhaust downpipe and coolant crossover pipe warmed the cable and thawed it. I drove it like that for a while, then it eventually suffered the same fate yours did. I have one of the RD cables from prior to when he started putting the rubber boot on them. It's been on there for probably 15 years.
A previous owner of the 86SE installed a PullPush Brand cable from an auto parts store. It has a boot on it, but the drawback is that you must adjust the cable to the proper length to get it to shift properly. It performs very well and hasn't lost adjustment. It may have the nut LocTited on.
