Well in case you didn't get your answer yet, here it goes.
I've sent a few units in, but not for problems just for my piece of mind on newly purchased used units.
The answer is it depends on what they say when you get your call.
For example. If the coil needs to be retuned or rebuilt, at least 7 days from the call if they start the process as soon as they hang up. Takes a lot of time to dig out and redo and let set the epoxy. Not their fault, it's the way of the beast.
But if this happens, which is the longest process that I've run into, just know that when you receive it back not only will it be a like new coil (functionally) but if it's a preset GB unit, they will set all the internals to that "new" coil.
When you receive something repaired back from Tesoro you can rest assured that it will come back with the same functionality as a brand new unit.
On a side not, even though my rare original cutlass (not cutlass II) Micromax seems perfect and only had one original owner before me, I want to send it in just to be safe.
It's literally a compadre at 12khz but with both a click down all metal (bypass disc circuit with still being a beep and not threshold based) which is more wide open then my modern compadre but also has a sensitivity knob.
I can't even find an ad or catalog that has it, but it exists because I have it lol. The cutlass II went to 10 khz like the modern silver Micromax.
But at any rate, just know that they dont sit on detectors and whatever needs to be done, as long as you agree, will be done in the most timely manner possible and what you receive back will be as close to brand new as you can get.
If I had a 7" compadre I'd send it with the 50 just to have a "new" one.
Let us know what you choose and how it works out!!!