Am grateful for your thoughts Rtb. "Noooo" is what I was thinking too.
In retrospect, a belt & braces film of oil/grease (or petrotape !?) might have been wise, but that wise thought didn't come to me. Too late now.
When you say petrotape, do you mean PTFE tape (sometimes referred to as petrotape) or the gunky stuff used for lagging steel pipes? Surely not the latter ?!
I can't find any markings on cylinder so it will be a generic Chinese item.
Update:
Warranty optimism ill-founded. 1st offer from supplier was a 23% discount (new cylinder at cost price, apparently). Of course, I thanked them, but politely declined the offer and suggested free cylinder, but offered to pay for "postage" and self-install, as a gesture. Response: "Obviously that wasn't good enough for you so we withdraw our offer." - also - "In your case we think that the rust happened because of a lack of maintenance (no oil applied; stored under a cover). Any piece of Chrome would start to rust under that condition."
The current situation: I have pointed out to supplier that their Operator's Manual makes no reference to oiling/greasing cylinder shaft for winter storage AND that their manual does actually recommend use of tarpaulin for outside storage. Response awaited, but I'm no longer optimistic.
What a pain: the mower is very well built, but seems that I've found its achilles heel.
Edit: thinking I might not want a direct replacement at any price (although mine might just be a rogue), but, so far, haven't found a supplier of cylinders, with threaded ends, to match the existing. Hopefully I can resume a "grown-ups" discussion with supplier to get a better price on a replacement and then maybe consider having the original (spare) cylinder shaft re-chromed properly for a trouble-free life (more than 1 winter at least!).