I think leadfinger is on the right path here.
Stretching a UT spring will kill its temper and ruin it and besides that is working on the symptom, not the problem. No offense to the poster (who is probably well-intentioned) but that's about the worst idea I have seen in regard to Microtech 'repair'.
The problem is elsewhere in the mechanism, an obstructed track or gunk in there. The properly functioning UT will work smoothly with the same effort both deploying and retracting.
Get ahold of a tri-wing driver set and open it up. You'll be able to figure it out in short order