Whirlpool electric dryer; problem with heat/thermal cut-offs (no heat)

I have a dryer, it's an electric Whirlpool, approximately 5 years old and a "common" consumer model. It's not top-of-the-line or anything of that nature.
Last week the heat in the dryer just stopped working. It would continue to spin but there was no heat. I checked a few places online to troubleshoot what was going on, and eventually discovered that one of the two thermal cut-offs was open (blown). I went to my local appliance parts store, purchased a new set of thermal cut-ffs (a high and a low came in the same package for about $25. I installed the low cut-off, which was the one that went out, and things seemed to be working fine.
While I was at the appliance parts store I asked the attendant if there were any common causes for this going out, and she said the majority of the time it is due to some kind of airflow problem.
So I checked the lint trap, the intakes/blowers inside the dryer barrel, etc, etc. I then had my girlfriend start the dryer while I was outside so I could check the airflow to the vent outside. Everything *appeared* to be working perfectly. If there was an airflow blockage, I certainly couldn't tell it via convential means.
In any case, I used the low heat and medium heat settings for a few loads that I had to do, and everything worked fine. I then ran some jeans last night and needed the "high" heat setting. I went back downstairs after the buzzer sounded to discover my jeans still pretty much soaked. Once again, it appears the heat has gone out. I haven't pulled it back apart yet, but I'm going to assume that once again the low thermal cut-off went out again.
My main question is if anyone knows why this might be occurring? The exhaust vent to the outdoors is actually quite long, so I have no good way to "look" into it to see if it's blocked, but as I mentioned above, it honestly seems fine.. plenty of air is reaching the outside vent, which indicates to me that there's no significant airflow problem.
Also, it seemed to me that after I repaired the thermal cut-off last time, when I used the "low" heat setting the first time, that the heat seemed pretty warm. I can't say whether it was much warmer than it had been previously, but it just seemed warmer than a low-heat setting should be. Once again, I have no real evidence saying this was the case, it's just a suspicion.
Are there any other common parts that may be causing a problem here? The heating element appears to be in good shape. I didn't replace the "high" thermal cut-off while replacing the low, because it wasn't broken. Could that have anything to do with it? Anything else to look at or check?
Last question might be: Any good places online to buy these parts? I didn't think $25 was too bad for getting the low and high thermal cut- offs in the same package, but then again, that's pretty expensive if I'm going to be replacing it more than once.
Thanks for any replies.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Mike wrote:

Hi, Usually those sensors are self resetting. If it is permanently damaged(burnt out), I wonder if the heating element is over heating by some reson like short or something. I'd clean out the lint build up inside the dryer as much as I can and disconnect vent, cover the exxhaust with an old nylon stocking and run a load to prove if air flow is the problem or not.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.