I'm the opposite of you in that my injuries and niggles have all been on my right side in recent years. One of my goals during this quarantine time is to try to identify and address any imbalances, and generally just become more stable overall.

One thing I did some across was the FMS (Functional Movement Screen). https://www.functionalmovement.com/..._NoBleed_Digital.pdf

I haven't tried it, but it seems like a good program for addressing muscular imbalances.

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Strava

Who says that your GCT is "bad"? Who says that 48/52 is worse than 49/51, or even 50/50, or 55/45? Your body knows what its doing. Who's to say that your GCT isn't a function of the surface you are running on? A cambered surface is likely to alter your GCT, or some other thing that you can't change and your body has adapted to optimally.

More or less the worst thing you could do would be to try and conciously correct it. If you want to ensure that your mechanics are as good as they should be, then you could embark on a stability and mobility training program. Strengthen your trunk stabilizers, strengthen your hib stabilizers, improve your joint mobility, etc. As long as you do this in a balanced fashion (working ALL joints in all axis, in all directions), then all of that will likely ensure your running mechanics are optimal for you. You should only ever focus on a particular muscle group/joint at the direction of a qualified medical person.

Doing that may or may not result in any changes to ANY of the metrics collected by Garmin or any other run pod. And, even if NONE of those metrics change, that is not the same thing as saying that your running mechanics didn't improve.

All that is to say, the running metrics are horse-shit. There is nothing actionable in any of them.

How is your hip mobility? Tight left hip flexors will limit extension before toe off. Right side compensates by taking a shorter stride, causing the lower shank to extend into a heelstrike/overstride. You end up "riding" the right foot longer from initial contact of heel strike to terminal stance. Also, check your ankle mobility.

I'm nearly always 51 or 52 right. It's probably just how I swing my arms.

I was a short track speed skater for 8 years when I was younger and developed an asymmetrical arm swing because of it.