i graduated from the collar nonsense a couple of decades ago. ironically it took a chevy guy to explain to me how the helix on the intermediate gear worked. the thrust is down not up. i have made shims to take end play out of the shaft. if you have erratic timing more likely than not the intermediate shat bushing is wore out.
I have always used a piece of hydraulic hose just long enough to keep a little pressure between the 2 shafts. May not help anything, but it can't hurt either.