I just did a transmission fluid change last weekend. I had a bottle of Motorcraft XL-18 additive that I'd previously bought a couple of years ago. After I thought I'd added it I noticed a slug of solid material still in the bottle. On a previous fluid change, when I used the additive, I noticed there was a lot of small particulate matter that is assumedly an important part of the additive package. I went ahead and busted up the large chunk of stuff with a screwdriver best I could, and then used several flushes of fresh fluid to re-suspend it and rinse it out of the bottle and into the transmission. I don't believe the material could have gone bad in two years sitting on a shelf considering where it is intended to live when added to the transmission. I figured once in the transmission any solid materials will get more completely distributed by the heat and action of the gears. The car shifts great (Red Line MTL) + XL-18, so I'm not worried about it. Of note is that the instructions for the additive say to shake it well before use so it seems some settling of solids is to be expected. Anyone else have this experience with the XL-18 additive?