I'm going to be doing a trans oil and filter change on my 96 C4. I'm just musing as to whether to go to the expense of using a fully synthetic fluid. Had a look on the Opie oil website and I can get a "normal " ATF to the correct spec for about £40. Or I can get Motul fully synthetic again to GM spec for £10 a litre so a fair bit more.I'm happy to spend the money, after all it wont be done again for a while but is it overkill?