a time-sert kit or helicoil kit will do the repair OR you can TIG weld the stripped material back into the hole and drill and re-tap the threads. THE TRICK with doing the primary chain adjustment is to achieve correct chain tension at room temp...then insert allen wrench into the threaded adjuster post to hold it securely in place......and then and only then tighten up the locking nut. very few do and they torque the hell out of the locking nut which at the same time is turning the threaded adjuster post and immediately strips out the aluminum threads.
i'll make you an offer: ship it to me and i'll heli-coil repair it and ship it back. NO charge to help you out...just pay return freight. downside is the cover weighs approx. 7 pounds as shipped as i recall and would cost about $80 via USPS priority air to return to you. OR i can ship you over a heli-coil kit as i keep them in stock for such repairs. they're reasonably priced. USPS first class air freight about $16.