I would try a high mileage non-synthetic motor oil at the same recommended weight. It doesn't flow as thin as synthetic and may help with the situation. Worth a try anyway.
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When my old GMC started weeping between the engine and the transmission, I put half a bottle of AT205 in the crankcase oil and half in the transmission oil and it stopped leaking and has been fine to date. Then again, it would probably run fine on KY-jelly mixed with fryer oil. OTOH, my understanding is that some cars, like Toyotas and Hondas are well known for having issues if you use anything but the OEM tranny fluid so I would not even think about using any additive in one of those or anything with a CVT for that matter.
Having worked on tons of hoopties back in my mechanicing days, I've never found any stop leak product that actually worked.
I've never used any of them, preferring to fix the leak, but with the car market as it is right now and this being a new one to me, I thought I'd check into it.
A better solution, though, will be to simply park it in the garage and only pull it out for trips where the other two vehicles won't be suitable until we can replace it. For DD purposes, the hatchback and antique (literally, it's 25yo this year) will be just fine.
Chris