Another thought on compressing that spring...but it’s gotta be done with mirror off the car... Put it in a homemade compressor tool. Couple threaded rods, washers, nuts from hardware store. Maybe simple 2x4 block under mirror, and small piece of notched pvc pipe pressing down on the washer with another 2x4 on top of that. Slowly tighten the nuts on the threaded rod alternately to close up the 2x4 sandwich until the spring is compressed enough. You’re basically building a large jaw wood vice. $10 or less in material and some ingenuity. I’ve made numerous versions of this sort of thing to compress snowmobile clutch springs and scale based spring testers for rpm tuning...some springs have over 400 lbs of force though I built those out of steel instead of wood. Have made some for car suspension springs too. But that mirror has to be back on your workbench again for this concept to work.