I recently purchased a 1999 Toyota 4Runner with over 200,000 miles, I'm in the process of changing all the fluids. I an wondering if I should stick with conventional differential oil or switch to a group V ester-based oil like Redline to keep it leak-free. I have read that ester-based oils swell seals more than other types of oils. Money is not a factor, main concern is hopefully preventing leaks. The transfer case and front diff take 75W-90, the rear diff takes 80W-90.