would have oil change first off, check for any oil leaks if any then gearbox likely, also when change oil in gearbox catch it in a very clean catch can leave to settle overnight then drain off most of oil without disturbing the oil in the bottom see if any bts of metal or brown colouring in it, brown dirty colour can mean the plates have worn out a lot sometimes oil change will help it, do oil on autobox is better done by a garage as must know what to do the first time ie if not filled correctly will damage it, could also try a gearbox cleaning flush agent link below add to old oil before drain and run for a while like it,
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