I recently added 80/90 to my rear end in my 88 240 Wagon 5 speed. (took almost a quart-leaky pinion seal!) Now (and maybe this had nothing to do with adding oil) in the morning, when I start down my long driveway, the rear end snatches and clangs (my neighbor asked what the noise was). The noise then disappears completely as I head out for the day. Does not repeat even after sitting for a few hours, but will in the morning after sitting all night). I visually checked my u joints,my flange bolts are tight...could I have a posi rear...there is no tag...would the symptoms be like that if I did and failed to put additive in it? Can I get additive at a parts store, or have to use Volvo's? Help!! Anybody ever had a noise like this?? It sounds like spider gears (in my mind, at least).