Two years ago I purchased a 2010 Jeep Wrangler Unlimited. I've always had it serviced by the same trusted mechanic rather than a Jeep dealer. Six months ago, with a total of 70,000km on the clock the gears started to seize up when the gearbox was hot after a decent drive. The mechanic checked it and said the oil was clear, and could see no issue with it. It was thought that it was possibly my short legs in the longer seat on the clutch not reaching the floor. Six months later, bearing in mind the Jeep is used mainly off-road, dirt, rivers, bush and mountains, the gearbox is now popping out of gears when hot, it's also grinding in certain gears on longer hauls, so back to the mechanic. Now I'm told it needs a new gearbox, that the former owner or service centre has put the wrong oil in it. My mechanic has nothing on record of oils changing through him. The original dealer we purchased it from was a Jeep dealer, but has since closed. Do you have any suggestions on proving the dealer has used the wrong oil? Jeep has quoted $16,000 for a new gearbox.
There's no reason to be putting oil in the gearbox, so the oil should still be the original factory fill. If you want you could drain a sample of the oil and have it analysed to identify what it is. I suspect the problem is related to its heavy off-road use rather than the wrong oil being used.