Hey Ive got that same hip flexor issue.I hear ya about that being the biggest hurdle.My strength increases daily,but the hip flexord are so tight.I walked bent over for the last six years.Plus the nature of my work as a roofer has me bent all day nailing shilgles so Im well versed at tight hip flexors.One of the things I would do before work every morning was lay on my back on my tailgate and let my legs hang over the edge,man the agony.I find the new hip easier to stretch than the left one now but as soon as Im immobile that thing tightens right up.I also have to get out of the habit of sleeping with my legs elevated on pillows or curled up in the fetal position when on my side as these positions keep those flexors short.These positions were the only way I could get any relief with my OA.I remember 20 years ago doing full side and front splits,being able to hold my foot in the side kick position above my head like Bill Superfoot Wallace.Now I can barely lift my legs high enough to climb a flight of stairs or climb a ladder.Those days are over,time for a rebirth like you said.I know full splits are out of the equation but I remember the slow tediousness of stretching but I also remember how crucial it is.But oh the pain,the pain of stretching tight hip flexors.Keep up the good work.Time to get busy up in here.Peace.