I have had my GK for a few years. It seems, per the repair shop, that the fan has gone bad on my 700rb. Fans are usually warranted by MTBF (mean time before failure) at minimum should 20,000 hours. I know I have not used my amp for 20k hours. Amp is outside warranty but fan may still be within MTBF from the fan manufacturer. Who's fan do you use and what is the MTBF of the fan ?