First of all, let me say that it is pretty clear that Kellyco is trying to make the best of a bad situation. When I had a problem with a PI detector that Minelab will no longer support, K'co said that they would repair it if they had the parts required.
Here are the US "Big Three"
Whites, headquarters and factory in Sweet Home OR
Garrett, headquarters and factory in Garland TX
First Texas (Fisher, Teknetics and Bounty Hunter), headquarters and factory in El Paso TX.
Are these companies perfect - of course not, but last month I sent a CZ-6 made in 1993 to Fisher in El Paso for a noisy coil conmector and had it back, fixed in 10 days from mailing. My bill $55.
Whites has repaired several older machines for me, in every case the turn aroumd was less than two weeks and the bill around $100. They are famous for repairing anything that they can, even 20 -30 hear old stuff - even to the point of (with your approval only) using servicable parts from scrapped units where new parts are no longer available.
Garrett I have no personal experience of, but I read lots of stuff on this forum praising their customer service.
Minelab - I bought a new SDC 2300. It was defective - it falsed when brushing the coil against spiny brush - I called Chicago and they asked me to return it - "it's a well known problem" was the answer - they sent me a new one - paying shipping both ways - which I decided to sell unopened in the box it came in.
One thing I also might mention. In my experience, none of these companies are very good dealing with emails.... phone is the best way to interact and since the tech's are often busy, just keep calling back till you get them - they also aren't great at returning voicemail messages.