Some taildraggers have more weight on the tailwheel than others. One of my taildraggers (with a 2300 pound gross weight) imposes 475 pounds weight on the tailwheel, that's just the way it was designed. I carry an aluminum (ex VW Jetta) jack in the plane just in case, and when parked, I jack the tailwheel off the ground with a modified floor jack, to relax the springs.
To loosen a stuck phillips screw: get penetrating oil in anywhere you can, then warm the area up a little with a heat gun. Buy a diamond tipped phillips bit of the right size for the screw, or use "screw grab" on the screwdriver tip. If you can't find either of those, mix up a tiny bit of engine valve grinding compound, and light grease, and dab the screwdriver tip with that, where it engages the screw. Then, (with a wrench driving the screwdriver, if possible) tighten the screw a tiny bit, just so it moves, then back it out. If that does not work, you're authorized to curse, while you plan to drill and use a screw extractor - but that's really a pain up in the trim actuator area of a 150 tail!