E153 transmission problem highway driving [Archive] - Toyota MR2 Message Board

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I have a 92 Gen2 mr2 turbo with I believe an E153 manual transmission. I am currently running 4 bottles of Castrol Gt fully synthetic 75-90w gear oil. It shift smoothly daily driving but when I go out out of town driving about 80mph on the highway after about 80 miles down the road I notice it startes leaking transmission fluid from the transmission air vent. And my 3rd gear grinds now matter how slow I try to put it in 3rd gear. But when driving 70mph for a long time nothing happens. I don