The heating with a heat gun is a useful try, for softening of the old hardened grease.
Are your hinges worn? Open door to first detent stop, lift at the rear corner. No play whatsoever should be felt.
To refurbish door hinges, they must be taken apart. See picture. Pin is hammered out.
Clean out spiral groove, replace the brass bushings. As replacement for the OEM bushings with a flange,, a cut piece of brass tube and brass washers may be used.