First, the manufacturer's warranties.: They are what the manufacturer determines is a reasonable period for anything to go wrong in the way of manufacturing defects. You can't warranty what other people do such as modifications, excessive tinkering, letting the detector fall in the water, abusing the detector/coil, allowing batteries to remain in a long-storged detector that leak and cause damage, etc., etc.
Some manufacturer's warranties have been 90 days, some 1 year, 2 year, 5 year, and then there is the "Lifetime Warranty. I have said this before and I'll state it again, any "Lifetime Warranty" is only for the products made and honored by the owner/manufacturer at the time it is issued. I have seen several different brands offer a "Lifetime Warranty" through the years, and one of two things happened.
One, the company just went belly-up so that ended the company and there was no longer any warranty of any kind. It ended with the end-of-LIFE for the company.
Two, a company is sold/traded/acquired by another business or individual. The name of the company might remain the same, but it is still a different company Owner and follows the new, now current owner's warranty policies. You can go buy a Bounty Hunter that comes with a 5 year warranty, but I remember the day when they offered a "Lifetime Warranty" but even a product made and sold during that period of time lost ALL warranty with the change of ownership and the new policy.
Then we have to remember that while Tesoro was reasonably generous in their earlier years and did some repairs on detectors sent in by the hands of a 2nd, 3rd or unknown owner, repair costs are on their shoulder for parts and employee coverage to get things fixed. You just knew there had to come a time when Tesoro would start to enforce it's "Lifetime Warranty" to the original detector purchaser. It was necessary due to the costs they incurred.
Unexpected repairs.: It happens all the time, especially when it is associated with a delicate or technical electronic function. In this case were are looking at your search coils. If they leaked, you might know it. If they were obviously cracked, you'd likely know it. If the coil cable was shorted out, you might be aware of that as well. But how do YOU know if the search coil is "out-of-spec?" Search coils are an integral part of the overall circuitry and they have to stay within a certain 'spec' to perform properly. If they are not, you can lose depth, lose a lot of function, and most of all end up losing any detection at all.
Reasonable charges.: Well, $50 to fix the general things that were required is reasonable, and since they no longer make the search coils for your detectors, then they know what a reasonable amount might be to repair what you have since they can't replace it. Totally repaired and functioning properly is better than having a non-working detector just sitting around. If they don't make that coil, then it would mean doing the rebuild to restore proper function, or they could look for a used model, buy it and hope the coil worked and just swap the coils. Then you would get a used, non-serviced coil, and foot the bill for acquiring the used unit to rob the coil from. That could cost more.
I know you posted this on the Tesoro Forum, and personally I think it should have stayed right there. It might point out a grumbling you have about cost, but it also points out the fact that Tesoro did, or was willing to do, the repair service work on a model to make it functional. It points to the fact that we can buy any used product and hope things work fine, but if they don't, it is nice to have a manufacturer who will take care of the consumer. In this case, it appears that Tesoro was doing just that.
Personally, I always try to check out any detector I am interested in prior to purchase. If buying 'mail order' you have to trust the seller's description. In your case, it might be that even the seller figured the detector's coil worked okay because they didn't have the equipment and knowledge to check it out and learn that it was sub-par.
Just my thoughts.
Monte
