okay , I've been hesitant to join these conversations when they pop up every month or so, but I'll throw my dos pesos out there--
No company offers a lifetime warranty on their product and expects to do a lot of work on them. In my view, the main reason for a lifetime warranty is to show the customer the company has confidence in the quality of their product. They dont really expect to have a lot of the product coming in for repairs, and Im betting that's usually the case. However, the rabid loyalty of their users and the longevity and utility of Tesoro machines has become the issue-- These machines continue to be popular 35 years after they were made! Internet istes --eBay, Craigslist, and forum sales-- have also greatly extended the working life of these detectors and all of this has occurred over the past 10-15 years or so. I dont think anyone at Tesoro realized how long these old machines would remain popular and effective so their business model didnt account for doing all of the minor --yet time intensive-- work on these units- especially for 2nd, 3rd, and 4th owners of the detector. They tried to be accommodating to secondary owners (but were under no legal, moral, or ethical obligation to do so), but it became too expensive to continue to work on these machines for free. I commend them for doing it as long as they did but I dont think even Tesoro expected the "lifetime" to be so long on their detectors--they made the things too darn well!
Usually if you have a piece of electronic equipment thats 35 years old, it would be in a display case, re-purposed, or hanging up on a wall as art. The fact that you can still use a Tesoro after all of that time and still get it repaired and tuned up for 50$ (almost half of which is shipping) is nothing short of amazing. Try finding someone who will work on your 30 year old TV, phone, computer, stereo, CB, VHS (or Beta max!) video player, camcorder etc.
So if youre lucky enough to have one of these units as an original owner, good for you! I seriously doubt you'll need to send it in very often but if you do you'll be treated well and for free. If youre not the original owner, Tesoro has never promised you anything other than a quality product that they will fix regardless of its age and for a very reasonable price. Thats a pretty decent deal too and not one you'll find with very many other MD companies.
Anyway, thats the way I see it.