Thanks guys, this forum has been a life saver. I replaced my blower motor and the dryer appears to be working now. I bought replacement transistors for the old motor and they arrived today.

I want to repair the old blower motor and keep it as a spare, so I replaced the transistor. I tested the old transistor and it tests good. My question is the following: Is it possible that the transistor tests good at room temperatures, but fails when the motor is in the dryer and it is hot?

First time replying, but just completed my second repair. Dryer showed same symptoms about 2 years ago so I followed the amazing (and since, updated) advice of all the folks in this thread.
The first repair was a tear-down and replacement of the Q1. Everything was put back together and it ran like a champ for about a 18 months worth of regular use.
It's now showing the same signs. I followed the updated advice to just break it down and "reform the wave washer"* while ensuring the blower motor housing is attached as firmly as possible. Afterwards, I put everything back together without replacing the Q1 and she started right up, blowing hot like a champ.

I timed my total hands-on time working at a leisurely pace to be just under 1.5 hours. I had the detailed instructions on a tablet and used small cups to hold each set of screws, minding the order. Including time to re-check some of these posts, it took just shy of 2 hours. It's a very simple fix that anyone should be able to accomplish using the awesome instructions of those that came before me. My thanks to all of you for nailing this issue.

Good luck!

*I wasn't clear on what this meant until I saw the actual washer and I simply (carefully/slowly) bent it to exaggerate the curves that have likely worn down.