was discussing a leaking diff pinion oil seal with a local mechanic. His suggestion–add a teaspoon of brake fluid to the oil. According to him this will swell the seal and stop the leak. Truth? Fiction? Old wives tale? Snake oil?—
If you’re running synthetic gear oil, switch to conventional. My experience is that Amsoil runs through the diff like grease through a goose. I suppose conventional motor oil would have a good effect.
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IIRC from 20+ years ago, mine is a leather seal. Not gonna help much on that. 
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Well, it isn’t crazy. I have a siphon pump from Harbor Freight which works fine except after using it for gasoline it loses the plasticizers in the ‘leather’ and it won’t pump. I used brake fluid on the seal and it softened a bit and once again worked.
Possibly a similar chemical to what is many oil leak stop solutions from AT-205, Lucas Oil and others.
It is a bit of a Hail Mary but your fall-back is to just replace the seal.
Yeah, if it is leather that stuff won’t help but I don’t know how you will know that w/o pulling it out.
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The first time I drove the PrtyKty into work, I parked it against the curb, nose pointed down. After I returned there was oil leaking from the seal, a lot. I drove home slowly and gently and afraid. The car had not been driven in ten or more years.
I refilled it, jacked the rear end up and ran it a bit. Seal swelled and leak stopped. That “fix” lasted about 20 years (25). until I put the 5-speed in, it was right there in front of my face, easy to do.
LLoyd
It’s not what you look at that matters. It’s what you see.
Henry David Thoreau
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Barely on topic but I am visiting my son in Seattle. He lives a few blocks from the world headquarters of Bardahl. My wife asked me the significance of that and the only thing I could come up with was that when I was a kid starting out with cars, they were known for their oil additives. I suspect they have something to address the OP’s situation.
They all leak bodily fluids from every spot on the car. My son’s car spun out of control and hit a telephone pole backward. Every fluid holder on the car leaked; front to back. Just add fluid until it gets to be a big expense.
Even modern cars can sweat or seep fluids. But despite any reputation one wishes to curse these cars with, they do not have to be major leakers. I have an S2 that leaves no drips, and an S1 that leaks very little. The leaks can be fixed if you desire.
Tom
…and very few do.
Just showing off for my friends for a car tour that began at my house. I parked the TR4 (with a white tonneau) under the E-Type (with no drip pans).
The word chutzpah was heard.
This was a few months after an engine & IRS rebuild but the car is still mostly leak free 6 years later.
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I love this! I pine after a TR4 or TR250. And under the Jag. What a spectacle!
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Which reminds me: given the choice twixt another E, or another TR4, the Trumpet would win, hands down.
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The main problem with a leaky diff pinion seal, in my view, is that the oil drips onto the exhaust pipes below, giving off an evil smell that seeps into the passenger compartment (I usually keep the rear quarterlights open, which doesn’t help) and into your clothes. I’m sure it’s not good for the lungs either.
I’ll happily try the brake fluid suggestion!
Personally, I prefer the aroma of gear oil on a hot exhaust. 