The " no oil " in the lower unit seems to explain it all.-----Take lower unit apart for repairs as needed.----Might be cheaper to find a used lower unit !!
If the nut was tightened too much , you end up with the flywheel taper stretched well over the crank taper.----Factory puller and a bump with a hefty hammer pops them off.-----Release agents do not help here.
There is nothing " scientific " about changing from 24:1 and going to 50:1 in my opinion.-----If you are losing sales because the competition is at 50:1 the board room made the change.
Dealer friend said---" I love the new 4 strokes "---Folks make regular appointments for service.-----Don't need a super mechanic to change oil / filters / plugs.-----All good $$$ that 2 strokes never brought to the shop.