Unless your mechanic sourced an NOS asbestos rope seal he likely used a Best Gasket Graphtite rope seal. My 161 f-head rebuild used one & it failed immediately. Two factory stated facts about Graphtite, 1: it's so slick it can spin in the journal if an included "locating pin" isn't installed in the bearing cap, 2: unlike OEM asbestos seals, there's nothing in the core of the rope that swells when soaked with oil. My rebuilder did not drill in the locating pin, but I was not about to give Graphtite a second try.
The transmission could possibly leak at two places in the front. The gasket for the front bearing retainer, or out the input shaft hole in the bearing retainer. Gasket would be a poor install, input shaft hole would be over filling. My T-96 gasket set did not have a seal for the input shaft hole but I installed a felt washer there anyway. No seal was present on teardown.
Rear main rope seal..............either source an NOS asbestos rope, (sometimes on ebay & willysjeepparts.com) or a non asbestos Sabo rope seal from Brazil which has a woven fiber exterior & a core that's supposed to swell when soaked.
