When I took apart the seats one of the bolts that hold the seat back frame to the seat base frame broke off. I tried removing the broken bolt with a bolt extractor, heat and penetrating oil. No luck. So now I have a drilled out hole and no idea what to do. I can't get access to the back of the nut (the frame is closed behind and you can't even see the nut).

Can I get a strong screw to hold it (with lock-tite) or should I look at something like a helicoil or other options?

For others who might have the same issue I ended up getting a tap from Canadian Tire (8mm). It was really easy to use.
1. Drill hole (use lubricant while drilling)
2. Crank tap into drilled hole (use lubricant and back out 1/4 turn every 1 turn in)
3. Back all the way out and back in again to ensure threads clean
3. Screw bolt in



Done. That was easy!

Glad to hear it worked out for you