We strongly recommend using a GL-4 spec transmission oil in the Mitsubishi manual transmissions. This oil offers good protection for the gears and bearings against wear out. Do not use any oil that has a GL-5 rating in the transmission, for these oils will not give the best shift quality because the GL-5 rating is too slippery for the synchronizers to be effective for high rpm shifts.</SPAN>
There are several GL-4 gear oils on the market for you to choose from. Redline MTL is excellent for daily drivers & weekend warriors and those who live in cold climates while Redline MT-90 is recommended for road racing type service. Both of these oils have proven themselves as a worthy oil for those who want to shift fast, yet are also looking for long service life from their transmission. There are concerns about using Redline's Shockproof gear oil inside manual transmissions. While this is truly an excellent product, it has been found that the heavy paraffin particles are quickly centrifuged out of the oil and build up inside the center diff housing and around the synchronizers and inside of the gearshafts. After several oil changes this build up may block oiling passages inside the gearshafts that lubricate the needle bearings and may also reduce the overall effectiveness of the synchronizers. Therefore we do not suggest using Shockproof in the transmission unless the transmission is to be serviced often or a dog box.
Another transmission oil that works very well is Diaqueen Super Multi part # MZ313376 and it available at the Mitsubishi dealer. While this oil is strictly specified for the EVO-MR 6 speed transmission, it also works great in the 5 speed transmissions and we recommend it.