Northstar Engines and System Technical Discussion Discussion, Exchange fluids how often? in Cadillac Engine Technical Discussion; I have a 2000 STS I've owned for 5 years, currently has 140K miles. Still has original coolant, brake fluid, ...
Basically you're wayoverdue for coolant, and overdue for both brake fluid and transmission fluid.
This time, take it to a dealer and cough up the money for a "Fall Special" package if one is offered. The entire coolant charge gets changed, brake system gets flushed and refilled, and the transmission gets the new DEXRON-VI synthetic fluid.
Not cheap, but you will have the peace of mind that its done correctly as well as have a dealer work warranty and someone to fall back on if something's not right, and a complete coolant, brake fluid, and transmission fluid change is no fun in your driveway.
Coolant: 3-4 years
Brake fluid: 4-5 years (its hygroscopic and absorbs moisture)
Transmission fluid: 5 years/100,000 miles or so