Hi,

I have developed a difference in left and right leg strenght over the past year. My left
leg (I am a south paw) is stronger than my right and that is affecting my cycling and
even walking (a very subtle limp) due to possibly longer right leg.

I think the root cause is that my right glute, hip and hamstrings are not balanced.

However I want advice on home spun strenghtening remedies that dont involve gym work - ie
stuff I can do from home .. eg. yoga like. You can point to other web-sites that
may illustrate the relevant actions.

PS:
I am 45 yo. Male. 5'7". 140 pounds.
My riding history is about 3K kilometers and 23K meters elevation gain since start of year.
So decent enough base. But recently my right leg is the first to reach fatigue particularly
around the knee area.

Take a look at crossfit.com. Lots of bodyweight stuff on there that can be used to work on equalizing you leg strength. Also consider one-legged pedaling drills.

Leg length discrepancies can be addressed by a quality bike fitting.

Take whatever workouts you can think of and do them single-leg. Single-leg squats for example. Different jumps (i.e. plyometrics) can also be done single leg.

And only work the dominant leg as hard as the weaker leg.

www.crossfit.com is good indeed (as would be the bike fitting mentioned above)

And yoga: https://www.yogajournal.com/poses/

Pistol squat video: https://www.youtube.com/watch?v=MLBAbqEZIeU

You could get power cranks if you are serious about your biking. They are independent cranks that have some kind of differential between them to let each side spin independently.