My fan service procedure is here: https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1863828/#msg1863828
Useful, easy to miss or not find, bookmarked.
@tggzzz, @med, @mnen - thanks for the pointers. I skimming through the sixty five
pages of 2465 teardown thread and have been through the tekscope (and other lists). Truth is, the amount of information to sort through is rather overwhelming, and that has fed my tendency to rely on "don't fix it if it ain't broke" driven procrastination.
Given the noise and symptoms though, I clearly need to repair/rebuild the fan in both. If I don't I end up with a bigger problem. I am guessing that I also need to fix the fan control board on the 485. Both units need a recap and the 485 has, at the least, sticky pushbutton switches and a couple of burned out lights. And no sense in taking either of them apart and not addressing the recap.
Time for me to graduate from fixing TMxxx plugins and Tek calibration generators and take on more complicated gear, I guess. Will start sifting through the threads, figure out what I need, and build a plan of attack. I don't know which scope I will do first as it isn't clear that one is actually any harder to work on than the other.