The tightening screw for the main pole of my quantaray QSX 9002TM tripod broke very easily after I was careful to never over-tighten. Is there any option than sending the entire unit back to quantaray service? Will this break again?

I had the exact same issue. I found a snapper tubing clamp at an aquarium store that works perfectly. Do an internet search on "snapper tubing clamp" or "snapper hose clamp", you'll find many suppliers. These clamps are good because there are many sizes, they are fairly adjustable, and easy to release. I set up the tripod, slide/attach the clamp on the main pole right above where the screw used to be and tighten the clamp until it doesn't allow any sliding.
You might also get lucky and find an adjustable tube clamp at a bicycle store or music store.