Rdavwhitaker makes a fair suggestion about sending the VT 100 MkIII back to ARC for a check-up, which would include looking over the fan. I recommend raising the question with Calvin. Having said that, I checked the ARCDB web site and see that ARC introduced the MkIII version in the Fall of 2001. The VT100 was discontinued in 2006
So I suppose it's possible that ARC hasn't seen the amp for as much as 10 years, but it could be less. Your amp's serial number would help to pin point the important dates.
FWIW, Calvin previously advised me that the parts used in ARC amps are pretty robust and can last for 15 or more years. If he recommends sending the amp in, do so. But, IME, I do not like schlepping and shipping heavy amps around because of the risk of damage, most importantly to the amp and less so to my back. Also, I gotta believe that your amp will be off line for a couple of weeks while at ARC. So, it's your call, but I mention these points for your consideration.
Another possibility is to have the amp looked at by an authorized ARC service tech in your neck of the woods. Again something to think about. FWIW, my ARC VS-115 blew a bias resister a week or so ago. I spoke with Calvin and confirmed my amp was still under warranty. There's a local ARC service tech near me. He kindly agreed to come to my house that evening like an old fashioned Doc who used to make house calls. The tech replaced the resister in about 45 minutes. The service call was free and I was back in business that evening. You gotta love ARC!!!