Fobia,I have the exact same issue but for me even after warming it up for 10minutes it will not start with the push button. My unit has only 6 hours and it is 3 years old. I change the oil every year and the fuel with stabilizer. Battery is charged.
I can definitely feel the pull string hard at first and then it goes.
Let me know how the unit worked after the changes you did.
It all sounds normal to me. When you pull start the engine, it is supposed to feel difficult partway through the cycle, that would be the compression stroke. Also, 6 hours in three years at 10 minutes per run.....is a flat battery. You didn't mention if the battery is on a maintainer or if you had it load tested. You need to run the unit once a month for 1 hour and then MAYBE the battery would be charged enough. If the battery has sat idle, no running or charging for 24 hours, and it reads lower than 12.5volts it's time to replace it as it's getting weak. Keep us posted... Dutchy