well yea if it gets tighter theres something damaged, if you have to get it off then just keep turning and pick up a new shifter from the junkyard for cheap
leave the shifter on, tighten it back on so u can drive the car, next go buy a new shifter and install
option2 is use whatever u can to remove the old knob without damage to the shifter and get the right die and rethread/clean the threads http://www.google.com/products?hl=e...a=X&oi=product_result_group&resnum=4&ct=title
i think its 10x1.25 someone correct me if im wrong im to lazy to go look at my tap