if you were 21-years-old I would suggest going to see an osteopath, doing some core strengthening, and then working on your ITB and then some running drills on a treadmill. but if you are 51 and have only just noticed this then you could potentially do yourself more harm than good by trying to "fix" this. I would seriously consider leaving this alone.
it would help if you could get some video of you running, from the front if possible, or the back would be a decent 2nd best. I suspect that this is affecting your foot plant and we'll see some spectacular rotation in your lower leg as you run and that would give us an idea as to whether or not this is something that can be fixed or should be left alone.
and, if it's your right achilles that's been giving you problems, you now know why.
if you are determined to work on it, then its hip flexors, rotators, abductors and adductors you want to be working on. but you would need to do core work first, all hip and thigh stability comes from a good core.
you could also do squats, deep squats, with no weights. but you need to stand properly to get any benefit from this, and you also need to have done some core work first or else you're wasting your time.
on the front of your hips, about four inches below your belly button, there is a bone that sticks out right where that little cash pocket is on your jeans. when I say place your feet hip-width apart, I mean your heels have to be right underneath that bone on the front of your hips. not out on the side where your trouser seam is, but right under that bone on the front of your hips.
okay, so stand with your heels hip-width apart and your toes pointing slightly out to the sides, around 10 to 2 or 5 to 11 on a clcock face. the point of pointing your knees out is so that when you squat, your knees will go out where your toes are pointing and you leave a space between your calves for your arse to drop into. if you point your toes straight ahead there is nowhere for your arse to go when you squat.
now, keep your hands on the back of your head, your back straight, look up, and squat down as low as you feel comfortable. hold the low point for a second so that you don't bounce out of it, then slowly push your way back to standing up. the whole movement should be slow and graceful not rushed against the clock. repeat, a few times. don't do too many to start with but build up slowly to around 12 -15. do them twice a week.