I think my saddle is too low.

It is about 1.5 cm lower than the suggested height from my frame-builder, who did a very thorough set of measurements. I also have that sort of weak feeling when climbing hills seated, so I tend to stand up more often than I should have to.

However, if I raise it, it hurts on the left side. (According to the same frame builder's measurements, my right leg is slightly longer than the left, and he had taken this into account already for the recommended height). I never noticed it until I was measured, so it isn't extreme. But I think this asymmetry is part of the problem.

Anyway, I have kept it "too low" so that it doesn't hurt. It is more like my whole leg hurts, not just where I sit.

I've been using an otherwise very comfortable Brooks B17 for several years.

Is there anything else I should try? Are there any saddles more forgiving of leg asymmetry? I've also heard some people suggest rotating the saddle slightly, so the nose points a degree or two off center (which way would be better?)

Oh, I should mention I tried a shoe cleat shim, but it was such a disaster I had to take it out mid-ride.

have you tried a cleat shim? The problem is that shim addresses the bottom of the pedal stroke but makes the problem worse at the top. Depending on length discrepancy different crank arm lengths could possible be a solution. What hurts when you raise it?

If it doesn't hurt with the seat positioned "low," then it isn't too low. Go with what your body tells you, not what a number based on an average tells you. You are not everyone. My B17 is "low" too, and I have no pain, and actually can spin better. When mine was the "correct" height, I dropped to one side and had hip pain, back pain, and was less efficient.

Try Steve Hogg's method of positioning your seat height and you will most likely end up where you are now, "low." https://www.stevehoggbikefitting.com...ard-can-it-be/
https://www.stevehoggbikefitting.com/bikefit/2011/02/seat-height-how-hard-can-it-be/

I'd start with the old heel of foot on pedal, leg straight , ( Low or Heelless Cycling shoes ) and fine tune from around that..

you need tech links instead? fine .. suit yourself.. ..

What hurts?

Front of knee? Back of knee? IT band area? Quads? Butt?

Calf? Ankle? Foot? (this is fun-should I go on?)

The links I gave does just that, fine tunes the initial height based on how efficiently you can pedal. Not complex, and no formula.

I also have leg asymmetry. I use a shim, but that's not nearly enough. I use a saddle that's the exact shape and width of the bones of my pubic ramus, because that's what I perch on in my road position. My legs don't touch the saddle at all. Probably more help can be found by stretching, especially the hams. Look around for good cycling stretches or use these: IT Band pain (during ride)

Yes. Pretty much the whole left leg. "Hurt" is really an over-statement, but the sensation I think it suggests over-extension. Left glutius medius specifically hurts if I go what is likely too high.

I should do this. I seldom stretch, and am less flexible than a two-hour cold cadaver.

Thanks for posting those links. I have to admit I was skeptical because of his reputation for crazy stuff like iPhone polarity interfering with bike fit, and I couldn't tolerate the mid-foot cleat position, but the stuff about compensating and asymmetry I think is spot on.

I think I still sub-consciously favor my right leg (where my ankle break was), and there is a good chance there is some real asymmetry. (One weird consequence of being on crutches for 4 months is that my right arch no longer collapses like my left one.)

LOL Yeah, the iPhone polarity interference is right up there with tinfoil hats. I ignore all that. He has a lot of good ideas, but tht one is way out there.

15 minutes every morning before breakfast. It's the every morning thing that does it and the small time commitment is good.. Every stretch for 20 seconds, to the point of discomfort, never pain.

Pain and stress near where the tendons attach to bone is a warning sign, perhaps of over extending or over exerting the muscle. Tendons take an awful long time to heal.

It's not that rare among us older folks.

I recently fitted a Brooks Swallow to one of my bikes, and it hurt on my left sitbone due to the new hard leather. I could also be sitting on the cantle plate, I'll have to check that. Rather than just HTFU, I rotated the saddle a little bit at a time, moving the nose toward the side that hurt. That equalized the pressure on the two sitbone contact points.

Yeah, we just have to use our heads and experience, and take the parts of what these guys offer that actually make sense.

How important is frame size if the saddle height is correctly fit ?

If saddle height is correct, then the important thing is the LENGTH (top tube) of the frame. This will vary due to preference, flexibility, body proportions, etc. (For instance, if you have a short torso, then you'd want a frame with a shorter top tube.)