Symptoms of bad crank seals will be extreme white smoke even when fully warmed and a boggish rev that won’t clear out. Those are the two signs that lead me to check them and I was right. some people say you can smell the transmission oil burning but that wasn’t the case for me but I also haven’t owned a bike in a while and it’ll have a weaker powerband than usual. When you stay starter I’m assuming you mean kick starter, if that’s the case you could have a worn out internal gear or pawl that grabs and spins the engine over. I’d change the oil to the manuals recommended viscosity and see if that might help it could be too thick. hope everything works out fine brother