About to do a full trans fluid change on my 2000 Mountaineer 5.0 AWD (4R70W). I'm going to use Motorcraft Mercon V. I have seen reference on this forum about an additive that needs to be added to prevent solenoid seal swelling. What is this additive? Do I need it for sure? How much to add? Where can I get it? Anybody got a Ford P/N for it? TIA

 

I'm not familiar with the additive you mention.
The only additive I use in mine is LUBEGARD in the red bottle.

 

Your owners manual or dipstick should have the fluid for your trans listed. Mercon V is a synthetic fluid. There are additives for dextrin III from Lubegard and Smartblend to make it compatible for Mercon V applications. But I have never herd of a additive to prevent swelling