First off, what 450 is this? Pro 3GX?
I find that most of the time the main gear wobble for me isn't due to imperfect plastic molding (though it certainly can be; you can get whole batches of bad ones) - for me it's usually caused by the hub not being totally seated in the main gear. You said you took the screws off - did you take the hub out and re-seat it? Make sure you get it really snug in there by hand before you tighten it down with the screws. If it's a little bit crooked when you begin to tighten down the screws, sometimes tightening them DOESN'T flatten it out, but just binds it in at a weird angle, which puts odd tension on the gear, and warps it just slightly.
I'd be worried about the mesh on the tail gear, though. That should NOT be tight. You want that to spin very easily. That could even be causing your spins on takeoff, not your gyro.
I would undo the screws that hold the tail block into the frame, and remove the tail assembly as one unit (with the crown gears in place on both ends) and once it's out and disengaged from the autorotation gear, spin the whole assembly and see if it's free. It should spin with NO resistance. If you have resistance, either you've got some weird compression of the torque tube shaft (so take it apart and re-seat the shaft until it spins freely), or sometimes I find that the bearings on the crown (umbrella) gears are so snug that, although they spin fine outside the assembly, once the bearing and gear are mounted in the tail block, they bind up and make the gear hard to spin. For this, I remove the bearing from the gear and lightly sand the shaft of the crown gear until the bearing fits less snugly. Then it usually spins freely when in the tail block.
Anyway, just a few places to check to get started.