I have no connection to any of this, and agree written terms settle things quicker, while I also understand a reputation can be all you need to support it?
Looking at any kind of lifetime guarantee made by a "repair agent" let's call it for easy wording, my expectation would be for any work to be guaranteed for life, but not necessarily the components he has fitted or something failing due to lack of use or lack of maintenance. If you bought a car and left it parked up for two years, would you expect the manufacturer to get it up and running again under warranty? Or if they serviced it and then you left it for two years and the engine seized, would that be reasonable?
To me it's more about "is he being reasonable in his actions?" It does not sound like his work was faulty, it sounds more like wear and tear for short of a better explanation. So then did he do the work for free and just charge for the shipping and the new reg, or did he charge for everything, which to me would have been a tough one to swallow with a lifetime guarantee?
Ultimately we still won't know unless it's made public and once again - we can make out own minds up, because just now it's just speculation and sabre rattling with no real meat on the bone.
I'd also suggest we keep it civil and not personal, we don't need pistols at dawn
James