I'm 173 and the Icon is a perfect fit, I can place my feet flat on the ground when the chair is all the way down, head is at the right level for the pillow, and I picked up this foot pillow thing which made sitting SO much more comfortable - raise the chair a bit, engage the rocking function and lean back a bit.
At your height the Icon is probably the only one that would really be meant to accommodate you appropriately but with a foot cushion you'd have more flexibility with chair height. Don't know about the backrest size though, your head might end up a bit low on the seat back.
Its definitely worn down.
I have had great success with this amazing leather conditioner, called Leather Honey:
I used that on the seating area of my leather sofa (which my pup scratched/dug after returning back from a wet walk -- and wore down the leather!!) but it has been restored pretty good! Give it a try, and keep an eye on that wear, just keep it conditioned well to prevent further wear now
I think its the piston thats broken. https://www.amazon.com/Replacement-Hardware-Repair-Office-Cylinder/dp/B00CEZ1EOK this should help or just repalce the whole piston.
Late to the party, but do you have a footrest? All chairs are uncomfortable to me unless I have a footrest. I have this Kensington one under both my desks, and a cheap Amazon Basic one under my workbench. Kensington Foot Rest (Amazon)
Without a footrest I get pain under my legs where they meet the edge of the chair. (I have Titans now, but similar in design and I suspect firmness to the Hero) 6'3", 240 lbs, muscular. I have lower back issues, which these types of chairs deal with amazingly.
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Edit: Sorry, realized you were in the UK. Here is theAmazon UK link for metric folks.
Hopefully you saw this already, FrostbiteReaper, but Amazon has them back in stock: https://www.amazon.com/gp/product/B08CRXLXWC/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1