My negative experiences have been with a Stingray and an original Sand Shark, but here is a copy and paste from The TreasureBeachesReport blog, that illustrates that I am not the only one to experience this problem:
The Treasure Beaches Report brought to you from Florida's Treasure Coast.
"What is a liftetime warranty? You might think that if a metal detector manufacturer offers a liftetime warranty that means that you'll be able to get your detector fixed under warranty for as long as you own the detector. Think again!
I don't know what lifetime Tesoro is talking about when they advertise a lifetime warranty, maybe the lifetime of a fruit fly, but it does not mean the lifetime of the detector.
One person was motivated by the advertised lifetime warranty to buy a Tesoro detector, which he used primarily as a backup. He liked the idea of having a detector that he could get fixed without cost or problems. He also owned a variety of metal detectors made by most of the other major manufacturers and used a couple of those other detectors the vast majority of the time.
But "lifetime" to Tesoro did not mean what the buyer thought it meant! When he sent in his detector for repairs after years of using it only rarely, mostly having it around as a backup, after tracking the detector and finding that the company had received it a week earlier but having heard nothing from them, he called to see if it was shipped back yet. What he then learned was that in the past week they did not diagnose the problem but instead told him he would have to send in a deposit to have it fixed and that they no longer had a circuit board for that model and so didn't think that they would be able to fix it anyhow.
Evidently what lifetime means to them is the period of time that they maintain a stock of parts for repairs. When they no longer have the parts for a particular model, the "lifetime" is over.
I know of another case in which the same thing happened. The older detector was purchased under the lifetime warranty and when sent in for repairs was deemed too old, and they said they no longer had the necessary parts to repair it. When pressed about the lifetime warranty, they said there was white dust from corrosion in the unit and that voided the warranty. That was said after they had already admitted that they no longer had the parts to repair the unit, but it gave them an out. If the corrosion had voided he warranty or not, they still did not have the parts to repair the detector. I suspect you can find some hint of corrosion on any electronics of some age even if you have to use a microscope to find it.
My main point is that when you hear a "liftetime" warranty advertised, it probably means something other than what you think when you hear the term. Don't be fooled by that.".
The Treasure Beaches Report brought to you from Florida's Treasure Coast.: Search results for tesoro warranty
As for the models in question, I am sure you can email the blogs author to find out.