Chances are that the bushing in the exhaust housing is worn, pretty common, not much you can do about it…You can replace the shift handle oring, but chances are that won’t help much. The bushing in the exhaust hsg is not replaceable either. Im sure you could find a similar bushing somewhere, drill out the hole slightly and press in a new bushing… Sounds like you have the engine back together and running, I wouldn’t worry about the dripping unless it is really excessive. Try pumping more grease into the shift handle grease fitting, might slow down the drip for awhile…
Let the bushing wait until you do the next water pump job….