I damaged the tranny fluid cooler on my '97 4.6L over the weekend...hit a stump. A neighbor offered to look at it and found no damage other than the cooler and a bad leak from it. He replaced it for me at his shop, but replaced the leaked-out fluid with Mercon V (about 4 quarts). Will that cause damage to the transmission...the fluid in there was at least 7-8 years old and probably wasn't Mercon V, but I'm not sure of that. Do I have to now flush and replace all the fluid or can I drive it with this mixture without worry. Car has about 92K miles and no tranny problems before this.