Just wanted to do a check-in and follow up on this in case it's useful for any other poor soul who ends up with a years-long hammy injury.
In mid-September, I started seeing a new sports chiropractor who came at this problem differently from anybody I've worked with before. With his help, I've worked back up to ~30 mpw, and even more promising, have been able to pull off a few ~10 mile runs averaging low 7's for mile pace. I had been unable to do that kind of work before without having a ton of residual soreness and recovery time. This is really, really promising and I feel so happy about the strides I've made with this injury.
Anyway, some more puzzle pieces I learned in order to mitigate my injury:
I learned that my ankle dorsiflexion was terrible and probably leading to some of my problems up the chain. Chiro has me doing sets of ankle ABCs every day, where I'm really trying to make those little ankle muscles burn and get to the fullest range of motion. I've improved my dorsiflexion a lot in the past six weeks.
I've also been working on intrinsic foot exercises. (e.g.
https://www.youtube.com/watch?v=2OOJ9AQ1AEg
). My toe mobility was really crappy before and now it's better. These are hard!! But feel really good now that my feet are more in shape. It's crazy to realize how much I'd been neglecting my feet.
I suspected my glutes weren't activating properly and I had the classic dead glute syndrome a lot of runners have. However, I didn't really know what to do about it before. So before, when I'd do glute bridges, I was doing them all wrong. Now I realize I actually need to squeeze my glutes while I do them. I know that sounds so ridiculously basic, but this was actually a revelation for me and has changed my awareness of in terms of trying to use those muscles properly.
I do theraband monster walks (to target glute medius) and "mindful" glute bridges before and after each run now in order to wake those muscles up.
After each run, I do some trigger point massage on both of my calves with a tennis ball. One leg is crossed over the other so that I can get more weight into the ball (e.g. like this:
https://i.ytimg.com/vi/aAnF6q88mU4/maxresdefault.jpg
).
I also use the tennis ball to massage my tensor fascia lata (TFL) on my left side, which is the bum hamstring side. TFL is the top of the IT band. That process looks like this (http://redefiningstrength.com/wp-content/uploads/2015/02/tfl-tennis-ball-rolling-e1423810711792.jpg).
Lastly, we figured out that my left hip (the side with the hamstring issue) has really good internal rotation but bad external rotation. My right hip has the opposite problem -- great external rotation, but bad internal rotation. So I spend a lot more time on external hip stretches on the left side, and internal rotation stretches on the right side. The idea is something like this (though be careful with knees):
http://www.yinyoga.com/ys2_2.0_asanas_deer.php
I've also kept up with yoga on a regular basis and do lots of lizard & pigeon pose on the affected side. It feels amazing and really seems to keep me out of trouble.
Hard to know whether any of these things has been a magic key on it's own, but I'm pretty happy that this has helped me make so much progress, and just wanted to share in case it provides an aha moment for anyone else.