NM Pajero transmission light

While driving my 2000 NM Pajero at 60 km/h the dashboard transmission light came on, which indicated that I was changing driving mode, when I was in fact driving in automatic mode and had not engaged the 4WD lever to any position. The flashing lights stayed on for about three minutes before switching to the centre differential lock flash. After about another three minutes these lights ceased to flash. My dealer told me "it was probably a sticking valve in the transmission and that it should rectify itself as the vehicle gets older". At that time it was less than two years old, and three years passed before it happened again. To my surprise the dealer I consulted told me the same thing as I'd previously been told. On another more recent occasion while driving on a freeway at 100 km/h both transmission lights began to flash and there was a crunching noise coming from the transmission. I immediately stopped, placed the car in neutral and allowed the car to idle for a minute before engaging the automatic transmission. Both lights ceased to flash and I continued on my journey. The vehicle is now over 13 years old with 220,000 km on it, and has only once been used in 4WD mode for about five minutes. Is this situation likely to occur more frequently, and is a "sticking valve" in the transmission an expensive fix?