My son bought a 1996 Tacoma in 2016. Truck was 4x4, extra cab, 3.4L with 5 spd, only 89K miles. It need a few little things, nothing major. The previous owner was the son of one of my college friends; he said he let a local station take care of the maintenance.
Well, i was checking the coolant level, took off the radiator cap, and saw what looked like brown oatmeal. This Tacoma was from the "Toyota Red" coolant era, and apparently the station had topped if off with standard green. The brown slush was the result.
Long story short, I removed and cleaned the radiator and overflow, and backflushed the heater core and the rest of the cooling system for several days.
Got it all back together and refilled with Toyota Red and distilled water, and added a big piece of white duct tape to the radiator top with "Toyota Red Coolant Only" on it. I was able to get a generic Toyota Red coolant from O'Reillys Auto Parts IIRC.
He kept the truck for a few years and sold it in 2023, with only 129K miles on it. Never had any coolant issues while he had it.