Actually I do in the 7.3L. In the transmission, worked great. I did 1 full bottle instead of 6 oz (1/2) as advised by Frank.
Tried 6 oz first, but the full bottle made an even more drastic and speedy difference. Smoother shifts and a quieter ride is what I noticed.
Haven't done it in the engine yet, but it's recommended to use 4 oz per quart of oil... which would amount to a ton of the stuff...
A little difference in the Power Steering as well.
As it is a diesel, I suggest whatever amount you put, you leave it in there for as long as possible. At least 8k, since normal OEM OCI recommendations are around 10k.
Of course, as long as it hasn't been totally abused that would be the best way to go about it to get your money's worth, I think.
