inkredible

I have a 1992 SC300 5 speed with a W58 transmission. My transmission fill bolt is rounded from the previous owner. Also, the bolt that is in there is clearly a 17mm or 18mm. I bought new fill and drain bolts from Lexus.

I tried soaking it in liquid wrench and wd-40 in hopes of loosening it. I tried bolt grip sockets. They catch and bite into it, but the thing doesn't budge. I've tried a pair of groove lock pliers. Same thing happened, the pliers lock on, but the bolt doesn't budge.

Also, after searching I tried to fill from the top, but I could not get the bolts/screws to budge either.

Anyone have any advice on how to get this thing out.