sahtt

The transmission isn't designed for it. The lower gears are designed for climbing up hills etc., not for aggressive driving. The internals of the transmission adjust to the circumstances and shift accordingly, by manually shifting it you are causing all the gears/etc. to force themselves into place. Transmission could last another year, maybe another week. No cost effective transmission swaps exist. Trade for a 5spd sc300 or save money for a new transmission.