I bought a 2005 Terracan 2.9 Manual in the UK recently as a project (had to replace head as one of the injectors failed and nothing would remove it, the hydraulic puller left half of it in the head!) and replaced the oil in the diff with a cheap limited slip oil from Westway - mistake! Got diff shudder, being a glutton for punishment I ordered their friction modifier hoping that would help - another mistake. Eventually after a great deal of research and frustration about the lack of small quantities of suitable oils, eventually rang our local hyundai dealer - their answer was Castrol Syntrax LSD/Limited Slip SAE 75W140 Synthetic Gear Oil. Bit expensive but readily available in UK, put in 3 litres, diff shudder completely gone - at last!