Unhook the steering link and see if it moves then.
No movement: Then a small propane torch on the kingpin area.Grease gun, after you heat it a bit try turning and adding grease.Might free up in a few seconds or maybe an hour.
Too much heat at the top or bottom will melt any seals in there.
Severe cases require drilling and an acetylene torch and dismantling.
That motor has bushings top and bottom. These get full of dirt/rust/old grease. See if the torch will loosen it up. If not, you will need to pull the entire motor apart to get at the bushings.
I doub't there are any rubber seals in the midsection.
