Enviro EF3 Trouble.

I have an 18 month Enviro EF3 (the new ones have 2 year warranty, I missed these by 2 months) I noticed the convection fan on low makes a moaning noise, but on high noise goes away. What I have also noticed is the fan is supposed to kick in to a higher speed when stove heats to a certain temperature; it doesn't seem to do this anymore. Was wondering if this would be because the fan motor s going, or the sensor? I was thinking of picking up a new motor assembly, and installing myself, only question I have, there seems to be some sort of caulking, or tar around where the blower assembly and the main body of the stove meet, anyone have a clue what I use to seal this? I know this is a lot of questions, any help would be appreciated.

Has you stove been serviced

Pull both blowers and clean them
they might be full of dust bunnies

Well last night I turned my hopper speed to high, and my fan to low. I let the stove get really hot, the fan never switch onto high. I thought once stove got to 160F it would trip the sensor, and would disable fan control, and would shift fan to high to clear the hot air from inside the stove. This would lead me to believe the 160F sensor is gone. What does everyone think? Also can anyone confirm that when I turn the fan control knob to its highest, that is not as high as the fan can go, the fastest the fan can go is when the 160F sensor is tripped, and the stove turns the fan to extra High by itself?

Update--- I replaced the 160F sensor, now what happens if the 160F sensor gets tripped, the fan turns off totally, even if I try and turn it up with the fan control Knob. This is what is suppose to happen I am guessing, meaning the emergency over ride is suppose to kick the fan into extra high, no matter what the knob says. Well the override is disabling the knob, but the fan is not kicking into high. Anyone know what part I should try next to replace?

the rheostat AKA fan speed control

listed on our parts page
http://www.hearthtools.com/enviro_pellet.htm
PRODUCT: Enviro EF 2/3/4/5/Solas & FS Gas fan controller with knob
EF-045 -- $41.00

This rheostat is a little PC board that changes the voltage to the blower
it it gets hit with a surge in will screw up.

Also DUST effect them

Thats what I was thinking, will replace today, and let you know.