Adding in another suggestion for the white delrin / metal gear combo. It was standard on mine.
It sounds like you definitely want to reset the gear lash on the tail.
If you haven't done it before, here's how I was told by an MA rep.
Pull the tail box out, loosen the set screws near the torque tube coupler and push the black/white gear away from the metal gear (in the direction of the coupler).
Tap the white gear closer to the metal gear by tapping the tailbox on the table, using the coupler. Keep spinning checking for lash and tight spots, keep tapping in. Eventually you should have the gears just barely touching, with no lash. Tighten up the set screws and reassemble.
I would do that before flying any tail gear. Too loose and the gears risk a strip. Too tight and you risk an explosion? Even if the gears were made of unobtanium the heat/force that must add up when too tight must be fugly.
For more suggestions:
Not sure on the history/status of this stratus, but sounds like all shafts should be replaced if it hit the dirt. Paddles perfectly distanced from the head? How does the engine/clutch alignment look?
I got owned by engine alignment first time around with mine. Caused bad bad vibes. My fan runout was .001 but it didn't matter. Tightened the engine while it was idling to help ensure it was plumb but alas, helis can be a coldhearted mistress!