Gear oil question

Since I omitted replacing my gear oil plug washer and it resulted in a leak I will be replacing my gear oil again

Originally it had Mobil 1 in it as the wrench replaced all the bearings and seals in '96, the last owner had it serviced and they put regular Quaker gear oil in it with Slick 50 additive, my concern was if I went back to Mobil 1 I may get seal leaks, I changed to regular Valvoline gear oil but it doesn't seem to shift as smoothly.

Any opinions on putting in Mobil 1 again resulting in possible leaks or trying a different brand full synthetic?

Thanks

Jeff,
I had problems with the Mobil 1 in my 328. After about 8k miles the synchros started acting up and "crunching", and then the diff started chattering, on tight, parking lot turns. I switched to Redline 75w-90 NS synthetic, and all is well....for now. And the cold second gear thing went away, too.

It seems like good results are being reported by users of Redline & Royal Purple.

Wondering if anyone has tried Swepco recently?

JRV, I used it in my previous 308. Worked fine, but did nothing for the cold 2nd gear syndrome. But was otherwise fine.

Well, this weekend I noticed just a little bit of chattering in the rear end(much less than when I had the Mobil 1), when making a tight parking lot turn (90 degrees) and pretty hard on the gas. Not a huge deal, so I am not rushing to put in the additive....Have not noticed this in normal or spirited driving on the road yet.

Dave,

I'd put the additive in before the plates start chattering worse. Usually by the time you can feel them going slow the chatter almost never goes away, additive or not.

Regards, JRV

Okay, will take your advice and get the additive and put it in.

From what I gather from Fchat, Mobil1 is (generally) 10W30, therefore much much thinner, especially when the car is cold. This would explain the leaks you have. Redline 75w90 is much more viscous.

That said, as an engineering, I don't understand why a seal wouldn't fullfill its role: preventing leak without consideration of the oil behind...

Mobil 1 gear oil is 75W-90. the 10-30 is engine oil, although it's lighter than I would use in a Ferrari. Mobil 1 15-50 is a better choice for engine oil.

Then here is my next question: what would make Mobil 1 75W90 more leaky than Redline 75W90. Per denomination, specifications should be the same. What is the difference?