From the Saito Manual

Fuel should be 10 - 15 percent nitro with 20 percent oil, preferably fully synthentic

From the Morgan Fuel web site, CoolPower 10 percent airplane fuel (Not the heli blends) only contain 17 percent oil.

Now if you consider that you only go 1.5 tank fulls then it is unlikely that the oil content caused the problem so I would not be afraid to bet that it was either run lean and overheated pretty bad or over it's short life span it was run on fuel that did not contain enough oil. I also beleive the damage was done loing before you got it.

It also simply could have been a bad sleeve.

Now I have had several Saitos and if the price is not a big problem the CoolPower 30 percent Heli blends are the way too go with any Saito. They are 30 percent nitro and 24 percent fully synthetic oil and it will make these engines purr like the preverbial kitty cat. At one point I ran the same fuel as you are and it did well but I could never get the engine to run consistently well, since I switched to the 30 percent I have never looked back.

Sorry about having to give you the bad news...