350 tranny leaking in my 72

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So I finally got my truck back with the new tranny in. Drove it from the shop to my house, about 8 miles. Just went out for a smoke break and noticed a good sized puddle under the truck. It looks like there's a leak where the speedo cable comes in. Is there some small gasket there I can easily replace? Otherwise, I'll have to wait until the shop opens up Monday.