Steve
Putting a nut on the inside is not a recommended repair. I would put a heli coil in or go with a larger diameter bolt. Not the first time I've seen or heard of a stripped bolt hole having a nut on the inside of the case though. As far as the rear cover being siliconed on that is OK. Personally I hate the stamped rear covers. I replace them with a cover from Xtreme.
http://www.xtrememotorworks.com/Part...Cub-Cadet.html