Kroil is excellent/pricey... mixture of 50/50% acetone/ATF is better and dirt cheap.
soak with above 50/50% mixture overheat before doing anything else. then try impact on 36mm socket before going to heat method.
impact action breaks free frozen nuts with less chance of breaking. save heat as a last resort.
you may be pleasantly surprised next morning after soaking with 50/50% acetone/ATF overnight.