clubman 

I'd try something adventurous like filling with a little fish glue mixed with a dark stain. Fish glue stays pliable and will keep the moisture out of the fissures. These are tough saddles.

Polaris OBark

This?

Polaris OBark

I don't think so, either. That is why I am considering alternative explanations (like a mountain bike brake or shift lever conveniently nearby and at the same height). If the saddle was jammed under that handlebar, the gouge pattern is explained by someone shoving something in and out in frustration without regard to the consequences. (Not that my wife would ever do that, but she can do stuff like that.) I think that either something like that happened, or your lab equipment suggestion, or someone knocking it over on something and putting it back and hoping no one might notice are all more plausible than deliberate vandalism.

Polaris OBark

The "new" one just arrived from Amazon. The previous owner did a reasonable job of repacking it, but the wrench was bouncing around the box and the envelope containing the instructions was opened. The rails and leather look ok so I guess I will pretend it didn't happen, but I really hate Amazon. I keep having to re-learn this lesson. They can't allow free returns without this sort of thing.

clubman 

That's the stuff. I didn't realize it was for luthiers but it makes sense. I've used it for applying wood veneers to substrate when making or repairing furniture. You'd want to be careful that the glue doesn't 're-activate' under your favourite trousers.

RH Clark

You could overlay it with a thin piece of leather. The leather would have to be thin enough not to affect the flex of the saddle. Use Weldwood Original contact cement and you won't be able to remove the new leather. You apply glue to both sides and let it dry. When you make contact, it will not move again so you have to work from the edge and stretch the overlay as you stick it down. Lightly sand your saddle and wipe it down with alcohol and let it dry good before applying the glue.