Welcome!
What part of the country are you in? is it a 340 or a 440? (different carbs) it could be a plugged jet, or a missing or damaged o-ring, or just the carbs out of synch. other possibilities include low float setting, leaking fuel line (sucking air) or a bad coil.
As for injector oil, I use a good quality 2 cycle snowmobile oil rated for injection. Some people swear by synthetic oil, but I don't doubt 5w30 will smoke and it could be fouling plugs causing your bog issue. There is a proceedure to make sure the cabs and oil injection is sychronized that might help too.
Usually crank seals won't cause a bog problem, but it never hurts to have new seals installed.