I'm replacing the left axle seal on a '99 with automatic and when I removed the axle, I discovered a large threaded hole in the transmission housing above the axle. Hopefully it serves no purpose on an automatic? Searched Honda parts diagram and can't figure it out. I was concerned it was a fill hole that should be plugged but it's deep and after cleaning it out and probing it, looking at with mirror, I'm still suspicious and want to make sure my tranny is not contaminated and about to blow up

 

Yup blind hole. Might have been used in other applications or just left for any possible future applications.