I use Z-Max in my 260E and have to acknowledge that it does indeed
appear to work.
The most noticeable effect is in fuel consumption: I was getting 360 miles per tankful and now am getting 440 miles (highway miles, measured on trips from Wash. DC to NY). I have not noticed any major difference in the transmission or fuel system.
The Linkite is some sort of micro-molecule that actually penetrates the metal to keep it "wet" and very, very slippery, which is the explanation for the results I have seen.
I am still using it (and due for a refill) and will probably continue to do so.
I am also impressed with their guarantee to replace any Z-Max treated part that fails. Pretty cheap insurance for $35.00