what good advice! I did this once on my model E, but it was a few years ago. I'm sure it would do my model D a world of good too, as it spent a rather longish sabbatical at the crossfit gym, and I only got it back a month or so ago.
Actually not as difficult to do as you might think....20-30 minutes? The four bolts holding the fan sidecover in place come off easily...just make sure to capture the small nuts on the other side because they'll fall off and roll away if you're not careful.
Next time I do it, I'll wash the screen and outer fan cover in hot water rather than trying to vacuum. And don't forget to tighten the cords and clean the belt before you reassemble. Good luck. Sounds like that Model D can use the attention.