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Last year I brought home a neglected Duetto with multiple leaks. To see what was coming from where I cleaned about 10 lbs of crud off the trans & differential. The trans had other problems so I switched it out, filled up the differential, and started using the car, saving the pinion seal for another day. To my surprise, the rear substantially dried up. All I can figure is with the crud off and the vent fully open, the operating temperature dropped, the viscosity dropped, the internal pressure dropped, and, the leak stopped. 70ep
 

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I'll admit, my knowledge of such things is pretty scant but it sounds a little far fetched to me. I'm sure you checked but I have to ask: are you certain that the rear end still has fluid in it? Another possible explanation is that the gunk on the rear end was from fluid migrating from the transmission at speed?!? Whatever the case, I'm happy for you!

Bill
 

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Bill: Fluid level hasn't changed a mm. To correct myself I meant the viscosity may have stayed higher, not lower. 70ep
 

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Yeah, the heat/viscosity thing sounds a little more plausible when I reread it. I'll bet the original fluid was a different viscosity as well. I've heard of transmissions leaking like a sieve with Redline fluid and the leaking stop with a different fluid. Might be a similar scenario with your diff.

Bill
 

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I've heard of transmissions leaking like a sieve with Redline fluid and the leaking stop with a different fluid.
My DD with a transaxle developed a leak at one axle seal shortly after I drained and refilled with Redline MT90. Put a new seal in when I rebuilt the CV joints and it still leaked. I'm now refilling with dino GL4 and hope the leak will go away when I get enough of the stuff in there. Maybe the thing to do is drain completly and refil with the dino but for now, there are other projects.
 

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Alfas are prone to leaks in many places when you change brands of fluids. The OEM rubber seals are really rubber, not the modern silicone alternatives. Rubber is sensitive to certain chemicals that are additives to some of the modern fluids.

My worst experience was on a complete rebuild of the brake system. New MC innards, caliper seals and boots, etc. Changed to the newest DOT 4 (AFAIR) silicone-based fluid. In two days I had NO brakes at all, which I found out as I was returning from a test drive and coasting into the garage.

**** the little bump on the Duetto's nose is hard to repair!!

Seems that the silicone-based "new" brake fluid had hardened the new rubber MC seals. Hard as a rock. Then I found an article in a car mag about the mis-use of silicone brake fluids.......

So I learned that "Experience is what you get when you don't get what you want!". And did the brake job all over again, but with the mineral-oil based DOT 3 (OEM) brake fluid.

Later alfas have changed to the modern silicone based seals and this problem goes away. Lots of the replacement parts for the older models are also modern material.

Silicone seals do not have any problem with any of the fluids or additives.

Except that I get leaks from anything Redline too.

???????

Robert
 

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70ep, this is funny--I had the same thing happen to me a couple of weeks ago. Noticing the leaks under the diff. I cleaned it up with a wire brush (about 1/4" of crud all over) and topped it off with NAPA HD 80w90. Checking it daily, I found no more drips. After a trip out to the Cape, a couple of hundred miles round trip, I checked it, found no drips and parked it overnight with a newspaper under the diff. so I could see if anything new dripped out, and found a small amount there in the morning. I'm theorizing that it only leaks from the pinion seal when under the pressure of high revs and that it took overnight for it to collect enough from the outside of the case to form a small drop on the newspaper. Will keep an eye on the level and try draining and refilling.
 
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