What I did was screw my knees up doing yard work. Now I can't run hard enough for the control thing to be an issue.
By the time it was a problem for me I was old and slow enough that those few stopped seconds didn't affect anything too adversely. I managed several marathons in those years in the neighborhood of three hours and at that stage of my life I was fairly pleased to have done that. So I just kind of rolled with the punch.
It did improve. The last of those marathons was the fastest. As I recall, it was only a problem on maybe 2-3 occasions in the second half of the race and it hadn't been nearly as much a problem in training.
I never figured it out but am pretty sure it was a circulatory or nerve thing. It also seemed related to effort, e.g, if I ran a hard six miles I might struggle with it after three miles or so, but if I went for a relatively easy 15-20 miler I might be able to run 12-14 miles before it was a problem.
Theorizing here, as you tire your form degenerates. If it degenerates in a way that alters your stride maybe it creates pressure on a nerve or artery or something. That last, fastest marathon (fastest for my masters years) came after I'd done nothing but distance work and moderately paced hill reps along with occasional races or time trials.
Have you tried a chiropractor? If I were going throuh this again I think that's where I'd start trying to treat it because I strongly suspect it's related to either circulation or impinged nerves.
One other thing that might be worth mentioning is that the problem was in my right leg and my right leg is noticably shorter than my left. That may have something to do with it.