Keep in mind that bushed engines such as the O.S. LA-series and the Thunder Tiger GP-series engines require a significant amount of castor oil as part of the lubrication content of the fuel. The ideal fuel for an O.S. Max .65 LA would be 10% Nitro and 20% to 25% oil content that is 100% castor oil. The castor oil actually helps "float" some of the engine components at speed to prevent excessive wear.

These engines offer adequate power for their size, they can be very reliable and very long lasting. Running these engines with 100% synthetic lubrication or 80/20 synth/castor fuel will chew them to pieces.

I believe the primary reason that bushing engines have fallen so far out of favor in recent years is that the fuel commonly available at most hobby stores simply isn't designed for these engines and getting good running results is almost impossible for novice pilots who aren't familiar with the fuel requirements for these engines.