What do I do about Automatic Transmission Fluid having been put into Differential Gear Oil reservoir?


I have a 91 Subaru Loyale with the 4wd clicker. I just got it. It’s an automatic (i’ve owned the manual before and loved it, but I’m less pleased with this auto).

Anyway, the guy that sold it to me told me about the “transmission leak”, said it wasn’t too bad, just top it off every couple weeks. It eats a quart every 3 or 4 months.

Well what I just realized is that it’s the “Differential Gear Oil” [DGO] that’s leaking, not the Automatic Transmission Fluid [ATF]. Furthermore, he’s been putting ATF where the DGO goes, instead of DGO.

What I want to know is - does it matter? And will it maybe stop leaking if i put the correct fluid in? I kind of doubt it will stop leaking, so I’d also like to know, will ATF with leak-stop possibly help with the DGO leak (assuming it’s okay afterall to put ATF in there).

For this car the owner’s manual specifies for ATF:“Dexron II” Type, and for DGO: API classification GL-5

Can anyone help me sort out these oils, what I can and can’t get away with, or any easy tips on treating this leak?


Get the ATF out of there now. If you do not, the final drive will fail. It is NOT ok to use ATF in the final drive.

It’s easy and cheap to change. Drain plug is on the very bottom of the final drive and it only takes a quart and then some to fill it up. You do not want the final drive to fail as that is very expensive and technically difficult to set up.

What has been the big problem over the years with Subaru is someone mistakenly draining the final drive by mistake; thinking that is the engine drain plug. They overfill the motor oil and leave the final drive dry. Usually within 50 to 100 miles the final drive gives up catastrophically.

There are only a few places the final drive can leak. The axle shaft seals which will be obvious visually and internally; which is not visible. This means the final drive oil is mixing with the ATF. The latter requires transmission removal and separation of the final drive from the transmission for seal replacement.

If this is an axle shaft seal problem keep in mind that new seals are directional. There’s a left and right side to them and they must go in the proper orientation. Gear oil will continue to leak but not as badly.
Lengthy but I hope it helps. Do the final drive ATF out/ gear oil in tomorrow if at all possible.