On the five speeds, the fifth Overdrive gear is not inside the transmission case, but in the tail stock. There is a replacement nut to secure this gear on the shaft, and it is not a large job to drop the drive shaft, unbolt the tail stock, and reposition the gear back on the shaft, then use the new much thicker nut to secure it. Cost is around $76 bucks for the improved nut and a new gasket, but you will also need several quarts of the special synthetic fluid at near $25 per quart. Another thing to become aware of, synthetic fluid does evaporate and needs to be checked, with any needed top offs every time you change oil and filter. More transmission repairs are caused by low fluid level than any other cause, and that gets expensive. Hope this helps.
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:woot
