I noticed that the rear end cover is leaking on my Grand Marquis (it was only sealed with RTV on the last service and no gasket was used, not the best idea... I know). Since a new gasket will be going on, I'd like to stick with a 75w90 synthetic as I'm looking for an extended drain interval. The car has 193k miles now, but it is running very strongly and I'm hoping to go another 75k-100k+ with it. In fact, I'm hoping to never touch it again after the new gasket goes on.
Mobil 1 is in the car right now, but I've also been looking at Castrol Syntrax and Valvoline Synpower. So even though this may not matter much, I'm curious to see if you folks if you have a preference (and perhaps a ranking) amongst these three. The other factor is that I don't have a limited slip (2.73 ratio and axle code C8), so there could be other ideas presented here, which I'm very open to. Based on everything I mentioned, I hope it doesn't make the whole post a total waste but I definitely appreciate the feedback, none-the-less. Thanks everyone.
Mobil 1 is in the car right now, but I've also been looking at Castrol Syntrax and Valvoline Synpower. So even though this may not matter much, I'm curious to see if you folks if you have a preference (and perhaps a ranking) amongst these three. The other factor is that I don't have a limited slip (2.73 ratio and axle code C8), so there could be other ideas presented here, which I'm very open to. Based on everything I mentioned, I hope it doesn't make the whole post a total waste but I definitely appreciate the feedback, none-the-less. Thanks everyone.