Does the letter give any hints as to why they are sending it to you guys?
It may have to do with the oil filter requiring a specified torque for installing. A number of people of who use to track Boss302's and switched to the GT350, had reports of oil filters coming loose while driving (off and on track).
Last October a friend with new GT350 had an oil related departure from the track at NJMP. Lucky he didn't collect anything before he stopped.
The FMC oil filter I believe comes with a thread compound on the threads of the oil filter, but the guy making the post had also mentioned that the correct torque was very important.
Incorrect torque on the oil filter and maybe early aftermarket oil filters that didn't have the thread compound may be the cause for some of the loose oil filters.
This is all gathered from the TMO.com posts that I have read and since I don't have a GT350, no real life experience except my friends issue last year.