I just sent in my F-75 for the upgrade. Mine is 9 months old and as of February'08 they changed the grip & battery compartment and fully weatherproofed the control box. They offered these changes to the holders of the older units for $50.
I called ahead and was given an return authorization number. Receptionist was pleasent and she directed my call to the repair lab. Spoke with a man named Felix and asked for the upgrade.
I got a call when they received the unit and were ready to service it from Felix again, who was very pleasant and we spoke for a while on the F-75.
Turn around was one week and I had a letter with the Fed-Ex tracking number two days before the unit arrived (Fed Ex home delivery).
The paperwork I got back said: "We have received your Fisher model F75 and based on our review of the product, we have determined that the product is in need of repair.
"Upgrade: $50
"Total Charges: $50
"We have tested your F75. We find it to be in perfect working order."
I noticed the coil I got back is spotless. I mean I can't find a bit of dirt or a scuff (It went and returned with a coil cover), even using a magnifying glass. I suspect they replaced the coil. The coil isn't serial numbered like a Minelab, so I can't say for sure - but if not I want their cleaning secrets. All works very well. I have absolutely zero complaints with Fisher's customer service.
The warranty on their new detectors is five years - which is better than the two years of White's, Minelab (only one year on the coils) or Garrett. The "old" Fisher was lifetime, as is Tesoro, and I think that is why there are murmors of dissatisfaction from the old Fisher owners. This is my first Fisher so I think five years is super!